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- C1 Sequence (Lexington/Pt. Pleasant)
Identification in Hand Sample
- Zoarium Morphology: Ramose and slender, smooth, cylindrical branches; infrequently dividing; diameter: 3-10mm
- Zoecia: Oval, oblique; thick-walled with thick interspaces; styles numerous, small; more oval/oblique in the more slender zooaria; more sub-circular in older specimens
- Mesozooids: Variable
- Monticules: Smooth surface
- Maculae: Present
Eridotrypa aedilis from the Arnheim Formation of Hamilton, Ohio (OUIP 1101)
- Description. – Zoaria dendroid with cylindrical branches, slightly variable in thickness, occasionally with conspecific overgrowth.
- In axial parts of endozones, autozooecia larger than in endozone peripheries, approximately parallel to branch axis for some distance, gradually curving outward. In endozone peripheries, autozooecia regularly intercalated, curving gently outward, locally slightly constricted or expanded. Autozooecia irregularly polygonal in cross section walls straight to slightly sinuous, occasionally crenulated locally. Basal diaphragms in axial parts of endozones sparse, occasionally common, commonly absent locally in some zoaria, evenly spaced in other zoaria and in zones of rejuvenation of autozooecia. Basal diaphragms regular, evenly spaced, in endozone peripheries. Zones of rejuvenation of autozooecia sparse.
- Exozones wide; autozooecia oblique or almost at right angles to zoarial surface, generally contiguous, mostly without preferred alignment, polygonal to subpolygonal in cross section, locally partly separated by mesozooecia. Autozooecial walls slightly irregular in thickness locally in early exozones, generally of uniform thickness in outer exozones. Autozooecial wall laminae distinct. Autozooecial boundaries well defined, narrowly serrated, straight to slightly sinuous, locally crenulated. Postules sparse, occurring mostly along autozooecial boundaries. Styles small, short, sparse to absent, with indistinct cores and sheaths, occurring mostly in autozooecial boundaries in corners between autozooecia. Basal diaphragms common to absent, planar to slightly curved, generally at right angles to chamber axis; occurring commonly, evenly spaced, in inner exozones, scattered or absent in outer exozones. Compound diaphragms and cystiphragms sparse, occurring occasionally in outer exozones of some autozooecia.
- Autozooecial chambers generally subelliptical, locally subcircular in cross section.
- Mesozooecia sparse to common, subpolygonal in cross section, with slightly moniloid proximal portions locally. Mesozooecial diaphragms irregular in thickness and spacing, slightly curved, locally coalescent. Mesozooecia commonly arising in inner and middle exozones in corners of autozooecia, commonly terminated in outer exozones by zooecial deposits, appearing as indistinct depressions in cross section.
- Maculae sparse, low, generally indistinct in cross section, commonly consisting of clusters of polymorphs with thicker walls and smaller chambers than those of autozooecia.
- The Wesenberg beds of the Russian Baltic provinces contain abundant specimens of the bryozoan well figured by Eichwald as Cladopora aedilis. The same species occurs less abundantly in the different divisions of formation D. Upon comparison these specimens are found to be identical with a very common, widespread American species, Eridotrypa mutabilis Ulrich, occurring in the Black River and lower Trenton strata. Dybowski has given good although somewhat diagrammatic views of the internal structure of Eichwald’s species (pl. 4, fig. 5), and these, in connection with the original figures, are sufficient for purposes of identification. As usual in this genus, and as indicated in the name applied to the American form, the surface characters particularly are somewhat variable. This variation is mainly dependent upon age. Thus, in Eichwald’s figure (fig. 137), the two fragments are of young zoaria in which the zooecia are elongated and separated by similarly elongated, shallow mesopore spaces. The other extreme,that of old age, is shown in Ulrich’s illustration (fig. 138 b). The internal characters are most constant and will serve whenever doubt is raised.
- Ulrich has given a detailed description, from which the following notes are derived:
- Zoarium of ramose branches 2 to 6 mm. in diameter, the younger examples slender and nearly cylindrical, the old ones more or less irregular. Zooecial apertures variable, the changes due chiefly to age, always oblique, the degree decreasing with age; walls thick, generally ridge-shaped, and highest posteriorly, sloping gradually down into the apertures. In young examples, also in old ones on which a new layer of zooecial tubes was formed, the apertures may be exceedingly oblique and drawn out anteriorly. With age, they become gradually more direct. The arrangement of the apertures is always more or less irregular, some of the short rows having six, others seven, occasionally eight, in 2 mm. Small maculae, either pitted or irregularly sculptured, commonly present in the older examples. In others, the maculae are represented by clusters of zooecia which, though a little larger than average, are distinguished from them chiefly by the greater thickness of the interspaces. The mesopores too are most variable, sometimes appearing to be wanting over large portions of the surface and at other times twice as numerous as the zooecia. As a rule, however, they are few, appearing at the surface as occasional shallow depressions between the zooecial apertures. True acanthopores probably wanting, but small knots at the angles of junction may be noticed.
- Eridotrypa aedilis may be distinguished from associated ramose bryozoans by its slender, cylindrical, infrequently dividing, smooth branches, with more or less oblique apertures and thick walls or inter-apertural spaces.
- Occurrence.—Very abundant in the Wesenberg beds (E) at Wesenberg (Cat. No. 44827, U.S.N.M.). Less common in the Jewe limestone (D1), Baron Toll’s estate (Cat. No. 57316, U.S.N.M.); in the Kegel limestone (D2), at Kegel (Cat. No. 57317, U.S.N.M.); and in the Wassalem beds (D3), at Uxnorm, Esthonia (Cat. No. 57315, U.S.N.M.). In America, the species is abundant in Black River and Trenton strata at localities too numerous to mention. The specimens figured by Eichwald and Dybowski were derived from the Wesenberg beds at Wesenberg, while Ulrich’s type-specimen came from the lower Trenton shales at Cannon Falls, Minnesota.
- British Museum, three specimens and on thin section from Russian localities.
- Smooth, cylindrical, infrequently dividing branches. Zooecia oblique with thick interspaces. Zooecia drawn out anteriorly (in younger specimens) and direct and sub-circular in older. Maculae present. Mesopores variable. Acanthopores represented as dark spots at junction angles.