Lambeoceras richmondense

Classification
Phylum: Mollusca
Class: Cephalopoda
Order: Actinocerida
Family: Gonioceratidae
Genus: Lambeoceras
Species: Lambeoceras richmondense (Foerste, 1917)

Taxonomic Details

  • 1917 Tripteroceras (Lambeoceras) richmondensis Foerste, Cincinn. Soc. Nat. Hist, pg. 44, plate 1, figs. 3A,B,C,D; pl. 3, fig. 2.
  • Stratigraphic Occurrences

    L.richmondense_strat

    Geographic Occurrences

    		
    Map point data provided by iDigBio.

    Stratigraphic Description

    Sequences (Formations)

    • C6 Sequence (Upper Whitewater)
    • C5 Sequence (Saluda, Lower Whitewater, Liberty)

    Identification in Hand Sample

    • Straight conch, strongly depressed in section
    • Ventral siphuncle
    • Transverse section lenticular
    • Dorsal and ventral sides of the orthoceracone are about equally convex
    • Rate of expansion of shell varies among growth stages

    Published Description

    Flower (1946):

    • Conch straight, strongly depressed in section, with the venter slightly more flattened centrally than the dorsum. The rate of expansion of the shell varies among the different growth stages, being rapid at first, and later more gradual until the adoral part of the shell scarcely expands laterally. The earliest stage observed shows a lateral expansion of 16 mm. to 32 mm. in 40 mm., while an external mold of a more apical portion of the same specimen indicates that this rapid expansion began at or very near a blunt apex. At a region between a width of 34 mm. and a width of 40 mm. the rate of expansion decreases, and the shell expands from 34 mm. to 47 mm. in a length of 80 mm. The larger specimens show a still more slender form in adoral parts of the conch. One specimen (Shideler Collection, Pl. 45, fig. 4) increases from 54 mm. to 59 mm. in the 40 mm. of the phragmocone and to 65 mm. in the 75 mm. of the living chamber. A second large specimen (Earlham Collection, No. 6422, Pl. 44, fig. 4) shows an increase of from 60 mm. to 66 mm. in a length of 114. The largest specimen observed increases from a width of 67 mm. to 70 mm. in a lateral length of 134 mm. (Pl. 46, fig. 1)
    • The section of the shell is generally uncertain as specimens are often subjected to crushing. However, one small fragment in a good condition of preservation shows a width of 31 mm. and a height of 14 mm. which increases in 31 mm. to 43 mm. and 16 mm. Flattening is more marked in more mature portions of the shell but may be augmented by distortion. The height is 20 mm. at a width of 58 mm. near the base of one of our larger specimens where the shell does not appear to be distorted.
    • The septa are strongly curved laterally but nearly flat vertically. In the central portion the septum is slightly oblique in undistorted specimens sloping slightly orad from venter to dorsum. The sutures in early ephebic stages of growth show lobes on the venter and dorsum which are slightly different. On the venter the median lobe is deep and sharp, though rounded at its center, the appearance of sharpness being augmented by the way the suture is curved laterally, so that is becomes convex orad upon approaching the lateral saddle. A broad rounded lobe, broader and slightly shallower occupies the entire dorsum, as shown in Plate 46, figure 3. Adorally, the difference between the dorsal and ventral sutures becomes less marked, the broad adoral convexity of the lateral part of the suture is lost, though in the extreme adoral portion of the phragmocone the extreme lateral part of the sutures of the venter again become slightly curved apicad, This is shown clearly on our largest specimen which represents a definitely gerontic condition.
    • The camerae increase in depth from 4 mm. near the apex at a width of 16 mm., to 5 mm. at a width of 40 mm. Adorally the camerae tend to become shorter. The largest specimen shows camerae 5 mm. deep at the center of the specimen, but only 3 mm. deep over a broad area near the base of the living chamber. Another specimen shows camerae 4 mm. deep at a width of 54 mm., and a third (Earlham Collection No. 6422) has camerae 3 mm. in depth at a width of 62 mm. In general, the depth of the lobe of the suture is equal to or slightly less than the depth of two camerae in the early part of the shell, but adorally the camerae are shortened and at a width of 60 mm. seven camerae occur in the linear interval of one ventral lobe, and are still more closely spaced in the extreme gerontic portion.
    • The siphuncle lies ventral of the center of the shell. The segments area broadly nummuloidal, as can be seen in several weathered specimens. The form of the segments is shown clearly in the enlarged sections. Horizontal sections are typical of Lambeoceras as shown from the genotype and the Cape Calhoun forms studied by Troedsson and by Teichert. In vertical section, however, the necks are more evenly recurved and do not extend apicad for any considerable distance along the siphuncle but are more similar to the septal necks of Armenoceras. Also, the expanded part of the segment is nearly equal to its length as a result of the reduction of the length of the septal necks.
    • The surface features have not been observed on this species. The living chambers are essentially complete on two known individuals, one of which has a maximum length of 90 mm. in the median portion, 73 mm. laterally, and expands in this length from a width of 56 mm. to 60 mm. The second living chamber has a maximum median length of 95 mm., a lateral length of 80 mm., and increases in width from 60 mm. to 63 mm.

    Foerste (1917):

    • Orthoceracone greatly compressed, transverse section lenticular, the lateral edges acute. Radius of curvature across the middle of the septa slightly more than half of the chord connecting the ends of the arc formed by the septa; for instance, the radius of curvature of the lowest septum preserved in the specimen figured is 28 millimeters, and the lateral diameter of the shell at this point is 53 millimeters. Along the ventral side of the shell the transverse curvature of the septa is somewhat greater than on the dorsal side, causing the suture line on this side to rise more rapidly than on the dorsal side until within a distance of 5 to 7 millimeters of the acute lateral angles of the shell, beyond which there is a slightly reversal of curvature. This causes the lateral parts of the septa to slope moderately upward from the dorsal toward the ventral side. The dorsal and ventral sides of the orthoceracone are about equally convex. The radius of curvature equals about seven-tenths of the chord connecting the ends of the arc formed by the curvature. The lateral sides diverge at an angle of about 7 degrees. The antero-posterior diameter of the shell is 20 millimeters where its width is 53 millimeters. From this point upward 10 chambers occur in length of 48 millimeters. The siphuncle, or at least the cast of its interior, is nummuloidal, the lateral diameter being 7 millimeters where the shell is 53 millimeters wide. The more exact structure of the siphuncle has not been determined.

    Lambeoceras richmondense from the Lower Whitewater Formation of Camden, Ohio (CMC 17160)