LAMELLIBRANCHIATA. 301 



above the hinge-line. Umbo moderately prominent. Umbonal ridge dis- 

 tinctly angular, extending from the beak to the post-basal margin. 



Test thin, marked by fine concentric striae, which are more or less fascicu- 

 late on the body of the shell, and very regular and uniform on the post- 

 cardinal slope. Interior unknown. 



The right valve in the specimen figured on plate Ixv, fig. 20, has a length 

 of 49 mm. and a height of 19 mm. A larger and better-preserved specimen 

 has a length of 59 mm. and a height of 22 mm. Another specimen referred 

 to this species has a length of 45 mm. and a height of 18 mm. 



This species differs from the others of the Hamilton group in its narrow ellip- 

 tical form, the regular curving basal margin, and narrow anterior end. The 

 hinge-line is comparatively shorter than in any of the species of the Hamilton 

 group except G. truncata. 



Formation and localities. In the upper portion of the Hamilton group, at 

 Geneseo, Livingston county ; at Bellona, Yates county ; on the shore of Cayuga 

 lake, and from a boulder of Hamilton shale at Sexton's, near the head of Seneca 

 lake, N. Y. 



GONIOPHORA CARINATA. 



PLATE XLU, FIG. 11 ; and PLATE XLIV, FIGS. 6-8. 



Cypricarditex cariiuUa, Co.vbad. Geol. Sui-v. N. Y., Ann. Rep., p. 53, plate, Hg. 21. 1841. 

 Sanfftdnolttes carinatux (Conrad), Hall. Prelim. Notice Lamellibranchiata, 2, p. 43. 1870. 

 Compare Cypi-ieardites Chemungensis, Vancxem. Geol. Surv. N. Y., Rep. Third Dist., p. 181, 2 ; p. 179. 



1842. 



Shell of medium size or larger, trapezoidal; length more than twice the height; 

 basal margin sinuate anterior to the middle, curving gently to the post-basal 

 extremity and more abruptly to the anterior; posterior margin obliquely 

 truncate. Cardinal line nearly straight and parallel with the basal margin, 

 equal to one-half the length of the shell. Anterior end sloping gently from 

 the beak and abruptly rounded below, limited by a broad undefined sinus 

 which constricts the basal margin. 



Valves moderately convex below the umbonal ridge, slightly concave on 

 the cardinal slope. 

 39 



