CLINTON GKOUP. 



67 



Fig. 3 a. Ventral view of a specimen having the cardinal extremities somewhat contracted, and 



ilie dorsal area vary wide and fully exposed. 

 Fig. 3 b. Profile view of the same. 



Fig. 3 c. A specimen with the dorsal extremities more extended, and the area broad. 

 Fig. 3 d. An individual much extended in width, having the cardinal extremities rounded and 



the area almost closed. 

 Fig. 3 e. A similar specimen, larger than the last. 

 Fig. 3f. A specimen with the hinge-line very much contracted and the angles rounded, with 



the area nearly closed. 

 Fig. 3 ^. A specimen which has apparently suffered no pressure. The beaks are approximate, 



the dorsal one much curved, and the area nearly closed. The cardinal extremities 



are rounded, and the whole contour of the shell very rotund. 

 Fig. 3 h. Profile view of the last. 



Fig. 3 i. Front view of the same, showing the elevation of the mesial lobe. 

 Fig. 3 j. A portion of the surface enlarged, showing the character of the striae. 

 Fig. 3 k. Ventral view of a larger specimen with the cardinal extremities rounded, the beak 



much elevated and incurved, and the area very small. 

 Fig. 3 I. Profile view of the last. 

 Fig. 3 m. Dorsal view of the same. 

 Fig. 3 72. Front view of the same. 

 Fig. 3 0. Dorsal view of a larger specimen, having the extremities rounded, and the beak much 



elevated and incurved. 

 Fig. 3 p. Ventral view of the same, showing the area nearly closed. 

 Fig. 3 r. Cardinal view of the same shell. 

 Fig. 3 s. Dorsal view of a specimen with the shell partially exfoliated, showing the direction of 



the dental plates. 

 Fig. 3 t. Dorsal area of a single valve, showing the narrow foramen. 



Position and localities. This shell appears in the iron ore beds and associated with strata 

 in Wayne county, and likewise in the upper green shale of the group at Sodus in the same 

 county. It is more abundant, however, in the upper limestone of the group at Lockport, 

 Lewiston, and other places in Niagara county. It is less abundant in the same position at 

 Rochester, and other eastern localities. It extends upwards into the Niagara shale (See Plate 



54 and description). (state Collection.) 



453. 24. ATRYPA CONGESTA. 



Pl. XXIIl. Fig. la- n. 



jitrypa congesta. Conrad, Jour. Acad. Nat. Sci. Philadelphia, 1842, Vol. viii, pag. 265, pi. 



16, fig. 18. 

 — — Hall, Geol. Rep. 4th Dist. N. York, 1843, pag. 71, fig. 2. 



Suborbicular, gibbous, often more or less ovate ; dorsal valve, much larger and more elevated 

 at the beak than the ventral valve, with a deep mesial furrow which commences at the beak, 



