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- C5 Sequence (Lower Whitewater)
Identification in Hand Sample
- Three loosely coiled volutions and wide-open umbilici
- Submature whorls depressed
- Fully mature specimens aperture length slightly exceeds width
- Anterior slope steep
- Lateral margins slightly explanate
Salpingostoma richmondensis from the Whitewater Formation of Richmond, Indiana (OUIP 1843)
- Diagnosis. – Shell moderately large (up to 50 mm long); submature whorls depressed, reniform, width about twice length; coiling loose; at maturity, aperture expands abruptly, extending anteriorly at much greater rate than laterally, so that aperture becomes longer than wide, anterior slope steep, lateral margins slightly explanate.
- Description. – Shell moderately large for genus, with about three loosely coiled volutions and wide-open umbilici; submature whorls depressed, reniform, width about twice length (length/width ratio 0.55), broadly convex dorsally, umbilical shoulders narrowly rounded, venter concave where contiguous with preceding whorl; at about 15-20 mm shell length, aperture expands abruptly, mainly anteriorly, so that in fully mature specimens aperture length slightly exceeds width (length/width ratio 1.11); expanded aperture widest posteriorly, reaching back to about even with posterior umbilical shoulder, lateral and posterolateral apertural margins flare slightly but do not recurve upward; anterior slope of expanded aperture steeply convex to or nearly to margin, generally flaring very little, anterior margin raised above level lateral margins in broad, shallow sinus; slit open from sorsum to just inside anterior apertural margin, the anteromedian closure being marked by shallow linear indentation; selenizone apparently developed on submature whorls; no shell markings known.
- Inner volutions depressed, transversely elliptical, width equalling slightly more than twice the height; lateral margins sharply rounded. In the latter half of the last volution the lateral diameter increases slowly, but the dorso-ventral diameter increases rapidly, so that the latter moderately exceeds former just behind the apertural expansion. The latter is abrupt, not very wide, narrower above than below. Dorsal slit about 20 mm. long, and located about the same distance back from the margin of the aperture. On the back of the second volution, where its width is 7 mm., are about seven irregular revolving ribs on each side of a narrow elevated slit-band. At intervals of about 1-5 mm., these ribs are crossed by transverse lamellae.
- Locality and Horizon. Richmond, Indiana, in the Whitewater member of the Richmond formation.
Ulrich & Scofield (1897):
- Shell slightly exceeding medium size, the height, including apertural expansion, 50 to 55 mm.; known from casts of the interior chiefly. These consist of about three strong volutions, the inner ones wide, depressed, sharply rounded on the sides, broadly and evenly convex on the back, less convex and with a very slight central cavity on the ventral side, the whole giving a transversely elongate subelliptical cross-section, whose width is a little more than twice the height. Dorso-ventral diameter of last volution increasing very rapidly in the outer half, while the transverse diameter enlarges very slowly. Just behind the apertural expansion, where the volution is more or less distinctly compressed laterally, the dimensions in three specimens (casts) are as follows: width 22, 23, and 24 mm.; height 26, 27, and 27 mm. At the opposite side of the shell the volution is about 15 mm. wide and 7 mm. high in all three specimens. The umbilicus is of the usual size for the inner volutions, but for the entire shell it is comparatively small. This is because the angular or narrowly rounded boundary moves gradually toward the ventral side of the voltions, causing the wall of the umbilicus to become more and more abrupt. Just behind the aperture it is nearly or quite perpendicular, the ventral surface of the volution being almost flat. Apertural expansion abrupt, apparently not very wide, with recurved edges, broadly ovate in outline, slightly narrower above than below. Dorsal slit about 20 mm. in length, beginning the same distance or somewhat more behind the apertural expansion. The slit is represented by a rough (fractured) ridge on casts. Behind it the cast is smooth, but in front of it there is a more or less distinct broad furrow.
- The surface marking have been observed only on the back of the second volution. Here they consist of about seven irregular revolving ribs on each side of a very narrow elevated slit-band. At intervals of about 1.5 mm. the ribs are interrupted by transverse lamellae. Where they are shown the volution has a width of 7 mm.