318 PALEONTOLOGY OF NEW-YORK. 



Fig. 3 c. Enlargement of the surface of this speoimon, showing the transverse and longitu- 

 dinal stria:. 



Fig. 4 fl. View of the spire of an individual where the peristome has been much expanded 

 on the side of the volutions. 



Fig. 4 6. Lower side of the same, showing the umbilicus. ( The peristome has originally 

 extended much farther, so as nearly to cover the umbilicus.) 



Fig. 5 a. A large individual of this species, showing the broad shallow sinus in the peristome. 



Fig. h h. View of the same, showing the sinus on the lower side of the shell. 



Fig. 5 e. An enlargement of the surface near the aperture, where the transverse striw have 

 become lamellose. 



PLATE LIX. 



Fig. 6 fl, 6. The specimen may be a compressed form of this species. 



Geological position and locality. In the middle portions of the Lower Helderberg 

 group, associated with numerous species of Brachiopoda : Albany and Schoharie 

 counties. 



Platyceras bisiiiuatuiii ( n. s.). 



Plate LVIII. Fio. 6 a, b. 



Shell small, obliquely subconical, arcuate, with a little more than a single 

 contiguous volution at the apex; the two first volutions rounded, 

 somewhat symmetrical when the dorsal portion becomes prominent, 

 and marked on each side by a narrow sinus ; while still later another 

 is developed on the right side, and which continues to the present 

 margin. 

 SuKFACE marked by fine lamellose transverse strife and obscure longitudi- 

 nal or revolving striae, and two strongly marked spiral grooves bounding 

 a dorsal lobe. 



Having but a single specimen of this species, its characters may not be fully re- 

 presented ; but it appears so different from any other in the collection, as to leave 

 no doubt of its specific distinctness. 



Fig. 6 a. The upper side of the spire, showing the sinus in the peristome, and the sinus 

 bordering the dorsal lobe : the extension of the latter, being broken off, prevents 

 the appearance of the notch in the peristome at this point. 



Fig. 6 6. The lower side, showing the sinus on the lower side of the dorsal lobe. The notch 

 in the peristome is exaggerated by the broken condition of the shell. 



Geological position and locality. In the middle portions of the shaly limestone, 

 associated with Orlhis and Spirifer, at tlie base of the Helderberg mountains, Al 

 bany county. 



