Formerly: Angellum cuneatum
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- C5 Sequence (Lower Whitewater)
Identification in Hand Sample
Cyrtodonta cuneata from the Whitewater Formation of Richmond, Indiana (OUIP 1863)
- The type Angellum cuneatum is numbered 8815 in the Faber collection at Chicago University. It is labeled as coming from Richmond, Indiana, and lithologically appears as though it had come from the Whitewater member of the Richmond. The specimen has been so strongly carved by some one who desired to clean the specimen, that its present form is more manufactured than natural. This is true especially of the part immediately anterior to the beak and of that part of the anterior margin where a cast of an anterior muscular scar has been carved out in a very unnatural location, far below the position which it must have occupied.
- The type evidently is a cast of the interior. The beaks appear to have been small and narrow. An angular ridge extends ventrally from the beak, in this cast, but disappears at a point slightly more than half way from the beak to the ventral margin. Anterior to the beak, a small but deep lunule has been carved out, and posterior to the beak a high hinge area is seen. It is evident that the greater part of the posterior portion of the shell is absent, but traces of concentric striae suggest that the shell was comparatively short.
- There is a possibility of Angellum cuneatum being related to Bodmania insuetum, a species also described from the Whitewater at Richmond, Indiana, (1894, Miller and Faber, Jour. Cincinnati Soc. Nat. Hist., 17, p. 23, pl. 1, figs. 5-7), apparently another Cyrtodontoid form, but the latter appears to have had more prominent and inflated beaks, giving it a much more broadly rhombic-cordate outline when viewed from the front. The attempted restoration of the posterior parts of this type, as shown by figure 3C on plate VII, may be regarded as a wild guess.
- Shell medium size, equivalve, much elongated from the cardinal line to the base, middle part subcylindrical, where width and depth are sub-equal; lower half wedge-shaped; umbones high, angular, and prominent anteriorly; beaks acuminate and incurved over the cardinal line; hinge line straight, short, and nearly at right angles to the longer axis of the valves. The cast is a little convex on the anterior side, where there is some evidence of a byssus, and slightly winged on the posterior margin. Surface marked by concentric lines.