318 
PALAEONTOLOGY OF NEW-YORK. 
Fig. 3 c. Enlargement of the surface of this specimen, showing the transverse and longitu¬ 
dinal striae. 
Fig. 4 a. View of the spire of an individual where the peristome has been much expanded 
on the side of the volutions. 
Fig. 4 b. 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. 5 b. View of the same, showing the sinus on the lower side of the shell. 
Fig. 5 c. An enlargement of the surface near the aperture, where the transverse striae have 
become lamellose. 
PLATE LIX. 
Fig. 6 a , b. 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 bisiiiuatiiin (n. s.). 
Plate LYIII. Fig. 6 a, b. 
Shell small, obliquely subcorneal, 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. 
Surface marked by fine lamellose transverse striae 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. G b. 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 Orthis and Spirifer , at the base of the Helderberg mountains, A1 
bany county. 
