202 PALAEONTOLOGY OF NEW YORK. 



Hyolithes singulus, n. sp. 



PLATE XXXII A, FIG. Iff. 



Form an elongated triangular pyramid, very gradually tapering from the base ; 

 transverse section subtriangular. The ventral face of the pyramid nearly 

 plane ; the dorsal face obtusely subangular in the middle, with the two 

 sides sloping in a gentle convexity to the lateral margins. The lateral 

 angles somewhat abruptly acute. Aperture and operculum unknown. 



Surface ornamented by fine, equal and regular transverse striae, which are 

 arched slightly backward on the summit of the dorsal face ; thence, curving 

 gently forward, are again recurved close to the lateral angle or suture line. 

 There are no visible longitudinal striae. 



The only specimen known is a fragment, which is imperfect at both 

 extremities, but sufficient remains for the generic determination, and the 

 specific characters are so unlike those of any other known in the rocks of New 

 York that it may be readily distinguished. It is preserved in a gray, calcareous 

 shale with numerous Brachiopoda. 



In its surface-markings it may be compared with H. stridulus of Barrande, 

 as shown on figs. 47-49, pi. 12 (Syst. Silurien du centre de la Boheme, vol. iii, 

 page 92). In this respect it differs from any American species which have 

 come under my observation. 



Formation and locality. In the calcareous shales of the Hamilton group, on 

 the shores of Skaneateles lake, N. Y. 



A single specimen of another species of this genus has been noticed among 

 the collections from the Hamilton group. The form is terete, gently curved 

 (perhaps from pressure), with an acute termination, and, so far as can be 

 determined, a circular or subcircular section. The specimen preserves a length 

 of eleven millimetres, and the margin of the aperture is apparently entire. 

 The surface is obscurely striated transversely. 



