Classification
Phylum: Mollusca
Class: Bivalvia
Order: Pterioida
Family: Ambonychiidae
Genus: Ambonychia
Species: Ambonychia radiata (Hall, 1847)

• Surface of the valves marked by strong, radiating ribs
• Ribs are crossed by fine, concentric, imbricating lines of growth
• Beaks acutely pointed and strongly incurved
• Anterior margin slightly concave
• Umbonal ridge evenly rounded

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Toni (1975):

• Material. – Five right valves, one left valve, two internal molds, two bivalve molds, and five incomplete molds. The specimens figured are 14303 and 16503.
• Locality and horizon. – South beach of Vestre Svartøya, Ringerike district; Holmenskjæret at Holmen, Tangen, Semsvannet, Jongskollen and Slependen in the Oslo-Asker district; Porsgrunn, Langesund-Skien district. Stage 5a. Gastropod Limestone, Ashgillian and Stage 5b, Calcareous Sandstone formation, Upper Ashgillian.
• Occurrence. – Originally described from the Lorraine Formation of New York. Recorded from the Maysville-Richmond in Quebec, Canada, also in Turin, Italy; and from Ohio, Indiana, Kentucky, Virginia and Tennessee, U.S.A. It is further recorded by Hind (1910) from the Drummuck Group, Scotland.
• Remarks. – This well known and widely distributed species is a common form in the Norwegian collection. The specimens at hand show the same characters as Hall’s species: Raised and incurved umbo, nearly obsolete anterior margin, obliquely truncate posterior side making an obtuse angle with the hinge line. The Norwegian species, however, seems to be larger than the American one. The specimen in Fig. 3, B has approximately fifty radial plications and is 29 mm long and 35 mm high.

Foerste (1924):

• Anterior margin slightly concave along upper four-sevenths of height of shell, owing to arching forward of the beaks and incurvature of anterior face of shell toward byssal opening. The upper part of the umbonal ridge never tends to be abruptly angular in a transverse direction as in B. richmondensis. Angle between the anterior face and the cardinal margin usually varies between 85 and almost 90degrees, but in some cases as low as 80 degrees. Length of the cardinal margin mostly about half the greatest length of the shell, from the beak toward the posterior part of the nearly evenly convex basal margin. In some, cardinal margin equals about three-fifths of greatest length of shell. Ratio of greatest width to greatest length, measured diagonally across the shell, from beak to posterior part of the basal margin, usually about 77 per cent, but may vary from 70 to 81 per cent. Convexity of single valve commonly not exceeding 6 mm in a shell having a maximum length of 36 mm. Shells exceeding 40 mm in length rare.
• The number of radiating plications varies considerably. Shells in which both cardinal margin and anterior face are well exposed frequently have 45, 46, or 47 radiating plications. Specimens occur which have fifty-five plications. In the specimens with forty-five plications, plications distinctly broader than the intervening grooves; in those with fifty-five, width of the plication exceeds that of the intervening grooves only slightly, if at all. Between both extremes intermediate forms occur in the same layers of rock.
• Wekwemikongsing Specimens. Numerous specimens of Byssonychia occur in the Lorraine exposure south of Clay cliffs , having about fifty radiating plicaitons. Umbonal ridge rather evenly rounded since the flattening of the anterior face of the shall, around the byssal opening, is very moderate. However, the general outline and convexity of these specimens resembles that of typical B. radiata sufficiently well to permit their reference to that species (No. 8517).
• Locality and Horizon. Originally described from the Lorraine formation of New York.
• Canadian Localities. In the province of Quebec it begins its range at the top of the Cryptolithus zone, Nicolet River section, St. Hugues, St. Hyacinthe, and Breault.
• In the Leptaena zone, in the Nicolet River section.
• In the Proetus zone, in the Nicolet River section, Chambly Canton, Vars, and Hawthore.
• Most widely distributed in the Pholadomorpha zone, occurring in the Nicolet River section, St. Hilaire, Weston, three-quarters of a mile south of Clay cliffs, and on the Bass Lake road south of Little Current.
• Similar forms, not known to be specifically the same, occur in the Waynesville in the Nicolet River section, at St. Hilaire, Huron river, Vars, Streetsville, 8 miles north of Meaford, and north of Manitowaning.
• In the Kagawong similar forms occur north of Manitowaning, west of the Indian village southwest of Little Current, and northeast of Gore Bay.
• In the Queenstown red clay shales, similar forms occur at several localities northwest of Meaford.
• Geographical Range. Outside of New York and the Canadian localities listed above, forms similar to B. radiata occur in the Maysville and Richmond of Ohio, Indiana, Kentucky, Tennessee, and Virginia. It is not certain that all of these forms are specifically identical with B. radiata of the Lorraine of New York, but at present all as a rule are assigned to this species.

Hall& Whitfield (1875):

• Shell small to medium sized, varying in outline from subquadrangular, with a rounded base, to acutely ovate, according to the degree of obliquity of the body of the shell to the direction of the hinge-line. Surface of the shell ventricose, and often subcarinate on the umbones and towards the beaks, gradually and somewhat regularly sloping to the basal margin, becoming attenuate and compressed toward the postero-cardinal region, and abruptly truncate and even impressed on the anterior side. Beaks acutely pointed, strongly incurved, terminal and projecting above the line of the hinge; posterior end at right angles to the hinge straight or rounded, or sometimes sloping obliquely backwards to the postero-basal margin; base sharply rounded. Anterior border of the valves excavated below the beaks, forming a rather large byssal opening, which is usually about half as wide as long when the valves are united.
• Surface of the valves marked by strong, radiating ribs, which are simple throughout, strongest on the body of the shell, and becoming finer on the postero-cardinal region. On the upper portion of the shell the ribs are flattened on the top, and often grooved in the center, giving them a strongly duplicate character, but becoming smooth below, the spaces between as narrow, or much narrower, than the width of the rib. The ribs are crossed by fine, concentric, imbricating lines of growth, which undulate as they cross the elevation.

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Classification
Phylum: Mollusca
Class: Bivalvia
Order: Pterioida
Family: Ambonychiidae
Genus: Anoptera Ulrich, 1893
Cincinnatian Species: Anoptera miseneri

Classification
Phylum: Mollusca
Class: Bivalvia
Order: Pterioida
Family: Ambonychiidae
Genus: Ambonychia
Species: Ambonychia alata (Meek, 1872)

• Straight hinge line
• Strong, radiating costae
• Strongly defined imbricating growth marks/li>
• Very large posterior alation
• Numerous fine, crowded lines crossing all costae and the furrows between

• The type of Anomalodonta costata is numbered 790 in the James collection at Chicago University. It possesses 19 simple radiating plications but the original number may have equaled 24. Compared with Anomalodonta alata, the radiating plications are distinctly narrower and are separated by relatively broader interspaces, which on account of their considerable width appear comparatively flat. Anomaldonta costata is a smaller species, usually not exceeding 50 mm. in height. The concave curvature of the anterior margin and the sinuous curvature of the posterior margin are both less, and the latter can scarcely be said to be alate; both of these features are possessed also by Anomalodonta alata during its younger stages. The posterior margin of Anomalodonta costata rarely is well preserved but its direction is indicated frequently by the direction of the concentric striae upon such parts of the shell as remain. The type is labeled as coming from Cincinnati, Ohio, but the horizon of the species is known to extend from the Arnheim, where frequently it is common, into the Waynesville member of the Richmond. As in the case of Anomalodonta alata, one or two additional plications are intercalated occasionally along the hinge-line or on the anterior slope of the shell. The total number of plications may reach 27 or 28.

Meek (1872):

• Shell attaining a moderately large size, subtrigonal in general outline, compressed posterior-dorsally, and more convex in the umbonal and anterio-central regions; umbonal slopes ranging at an angle of about fifty degrees below the hinge line, and broadly rounded; hinge line straight, very nearly or quite equaling the greatest anterio-posterior diameter of the valves, and ranging nearly at right angles to the anterior side of the same; posterior alation very large, not separated from the swell of the umbonal and central regions by any defined sulcus, slightly rounded at its immediate extremity above; posterior margin faintly sinuous a little below its intersection with the hinge margin above, thence sloping forward and downward, and finally rounding into the regularly rounded base; anterior side more or less concave and nearly vertical above, but rounding regularly into the base below; beaks terminal, rather pointed, rising little above the hinge line, and directed a little obliquely upward and forward, with more or less inward curvature.
• Surface marked by 24 to 28 simple, strong, radiating costae to each valve, that are nearly equal in breadth to the furrows between; those on the central portions of the valves passing nearly straight from the beaks obliquely to the posterior basal margins, those on the anterior side curving more or less forward below, and those near the cardinal margin curving a little upward behind. Crossing all of these costae and the furrows between, are numerous fine crowded lines, and at regular distant intervals, a few strongly defined imbricating marks of growth that curve parallel to the basal and posterior margins.
• Height, 2.30 inches; breadth, 2.20 inches; convexity, about 0.80 inch.

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Classification
Phylum: Mollusca
Class: Bivalvia
Order: Pterioida
Family: Ambonychiidae
Genus: Anomalodonta
Species: Anomalodonta gigantea (Miller, 1847)

• Large pelecypod 8-10 cm. in length, 8-10 cm in width
• Radial plications broad, deep
• The beak is sharp, incurved, and situated at the end of the cardinal margin
• Byssal opening immediately below the beak
• Lack auricles

• Pelecypod. Characterized by its outline, large size, broad, deep plications, and tooth structure Richmondian.

Fossils of Ohio (1996) :

• The Upper Ordovician genus Anomalodonta is represented by A. gigantean Miller, a large species that lacks auricles and has broad, radial plications.

McFarlan (1931):

• An unusually large pelecypod 8-10 cm. in length and almost as wide, alate posteriorly and marked by 30-40 strong radiating ribs. Anterior edge about at right angles to hinge line. Beaks sharp, slightly incurved, and situated at the anterior end of then cardinal margin. Byssal opening immediately below the beak, 6-7 mm. in diameter. In a specimen 8 cm. long the hinge has a length of about 5 cm. From 4-14 cartilage grooves extend from the end of the wing to the byssal opening. A characteristic Richmond species known from the Arnheim to the Whitewater. In the region around Louisville it seems to be restricted to the Arnheim.

Miller (1874)

• Shell equivalve, inequilateral, alate posteriorly and compressed, more convex toward the umbones and the anterior side, anterior side abruptly declining, beaks rather sharp and slightly incurved. Surface marked by 30 to 40 strong radii, same width as the intermediate spaces, which are concave grooves marked with concentric striae, giving much the same external appearance as those of an Ambonychia radiata. Shell marked exteriorly, toward the margin, with lines of growth and concentric striae, which cross the radii, rendering it likely that concentric striae crossed the radii over the whole surface of the shell, though they appear now to be smooth. Byssal sinus immediately below the beak anteriorly, about ¼ of an inch in diameter in a large specimen. Height of the shell from 2 to 4 inches, greatest breadth about 1/5 less. Shell quite thick about the umbones and wing, but thinner towards the base. Large cardinal tooth or elevation beneath the umbones and sloping posteriorly from the beak. The cardinal elevation on the left valve having a depression to receive a corresponding elevation, though slight, on the right valve. From the cardinal tooth there are from 4 to 18 lateral cartilage grooves extending posteriorly to the end of the wing, and terminating with the shell, and there are the same number of cartilage grooves on the anterior side of the cardinal tooth that immediately run together as the pass into the byssal sinus. The cartilage grooves vary in number with the age and size of the shell. The shell is thickened on the anterior side, and appears to show lines of growth passing through the sinus to the base. A large muscular impression is found near the anterior margin, half way from the sinus to the base of the shell, and there are appearances that indicate another muscular impression on the posterior wing of the shell near its termination. Greatest depth of a valve in a large specimen, ½ and inch.
• This is the largest bivalve yet known in the Cincinnati group. It may readily be distinguished from Anomalodonta alata by the surface markings, though the general outline form of the two shells are nearly the same.
• I found this species near Versailles, Indiana, about 40 miles west of Cincinnati, and about 300 feet below Upper Silurian rocks; and I also found what I believe to be a cast of the same at Richmond, Indiana. I do not know that it can be found elsewhere, but the probabilities are that it can be found in the upper part of the Cincinnati Group, from Madison to Richmond, and at other places.

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Classification
Phylum: Mollusca
Class: Bivalvia
Order: Pterioida
Family: Ambonychiidae
Genus: Anomalodonta Miller, 1874
Cincinnatian Species: Anomalodonta gigantea

Classification
Phylum: Mollusca
Class: Bivalvia
Order: Pterioida
Family: Ambonychiidae
Genus: Ambonychia
Species: Ambonychia robusta (Miller, 1880)

• Shell is large, very ventricose. Distinctive narrow radial plications.
• Beak acute, triangular
• Anterior side flattened and depressed
• Muscular impression high in this species

Davis (1998) :

• Pelecypod. Large, imperfect specimen, showing convex form and distinct plications. Waynesville to Whitewater.

Fossils of Ohio (1996):

• The genus Ambonychia, which ranges from Middle to Upper Ordovician, is represented in the Ordovician of Ohio by A. robusta Hall. This medium-sized species has narrow radial plications.

Miller (1880) :

• Shell large, very ventricose, anterior side flattened and depressed in the region of the byssus; beaks acute, triangular; posterior wing, short, muscular impression high, and surface marked by about forty simple radii, which are crossed by fine concentric striae.This species is distinguished by its large size, triangular beaks, flattened and depressed anterior side, and high position of the muscular impression. The specimens are quite variable in size, but a medium specimen has a” height from base to beak of 2 6-10 inches and thickness of 1 8-10 inches. Specimens having the shell quite well preserved, occur in the upper part of the Hudson River Group, near Osgood, Indiana, where I collected the type specimens. And I refer the large casts having a flat anterior side, which occur at Richmond, Indiana, to the same species, though the*y have a greater height in proportion to their length and thickness.

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Classification
Phylum: Mollusca
Class: Bivalvia
Order: Pterioida
Family: Ambonychiidae (Miller, 1877)
Cincinnatian Genera: Allonychia, Ambonychia, Anomalodonta, Anoptera

Classification
Phylum: Mollusca
Class: Bivalvia
Order: Myalinida (Paul, 1939)
Cincinnatian Families: Ambonychiidae