94 [Senate 



Fig. 14 & 15 illustrate the exterior form and characters of Leiorhynchus multicosta of the 

 Hamilton shales, and may be considered as illustrating the general external charac- 

 .ers of the genus. 



ADDITIONAL SPECIES FROl THE HAlILTflN GROUP. 



ATHYRIS CORA(n.s.). 



Shell depressed suborbicular or transversely elliptical, moderately gibbous : 

 valves, in specimens of ordinary size, nearly equally convex; length and width 

 of the dorsal valve about as eleven to fifteen, the proportional length of the 

 ventral valve being twelve or thirteen. Surface marked by concentric lamellose 

 striae or lamellae of growth, which have apparently been fimbriate in their perfect 

 condition. There are likewise a few stronger concentric ridges or grooves; and 

 there is a shallow longitudinal sinus in the ventral valve, and a. corresponding 

 elevation or flattening of the centre of the dorsal valve. In the casts, this mesial 

 elevation is marked by a narrow depressed line. 

 Geological formation and locality. In the shales of the Hamilton group at 



Delphi. 



SPIRIFER CLIO (n.s.). 

 Shell subrhomboidal, more or less gibbous or ventricose; extremities usually 

 salient, and sometimes extended into raucronate processes. Dorsal valve regular- 

 ly convex, becoming gibboTis; mesial fold strongly defined, simple at its origin, 

 and becoming flattened and grooved below the first third, or for a- greater 

 proportion of its length : cardinal line showing a narrow area. Ventral valve 

 more gibbous than the dorsal; medial sinus deep and strongly defined, with a 

 slight elevation in the centre, giving an undulation in the direction of the lamellae; 

 beak incurved; area strongly defined; length more than twice the height, and 

 extending to the cardinal extremities : foramen somewhat narrow, sometimes 

 twice as high as the width at base, open to the beak. Valves marked by from 

 six to ten or twelve regular plications on each side of the mesial fold and sinus, 

 more than half of which run out upon the margins of the area. Entire surface 

 marked by regular imbricating lamellae, which arc sharply arched at the sum- 

 mit of the plications and in the groove between them. 



This species has sometimes been confounded with 5'. zigzag; but the plications 

 are more numerous, while the mesial fold and sinus are marked by a groove and 

 elevation not shown in that one. The imbricating lamellae are coarser and stronger 

 in the S. zigzag. 



Geological formation and locality. In shales of the Hamilton group : at Mo- 

 scow, York and Geneseo, Livingston county; and at Darien, Genesee county, N.Y. 



