LOWER HELDERBERG ROCKS. 
321 
Platyceras retrorsum, var. almormis. 
Plate LX. Fig. 4 a, b, c. 
This shell resembles the P. retrorsum , except that it is more depressed on the 
upper side, and the aperture transverse. The lower side of the last volution is flat¬ 
tened and produced, the peristome on that side extending in a broad linguiform 
process much beyond the upper or anterior side, leaving a deep sinus upon the back 
of the shell. This peculiarity can scarcely be regarded as of specific importance. 
The upper side is plicate, and transversely marked by lamellose strise. 
Fig. 4 a. Upper side of the shell, showing the plications and the strong lamellose striae. 
Fig. 4 b. The lower side of the same, which is marked only by concentric lamellose striae. 
Fig. 4 c. An enlargement of the striae on the upper side. 
Geological position and locality. In the middle part of the Lower Helderberg 
group : Schoharie county. 
Platyceras intermedium (n. s.). 
Plate LYIII. Fig. 11. 
Shell arcuate subspiral, making a little more than two volutions, the last 
one free and becoming gradually straight. The apex is very minute, 
consisting of little more than a single volution with the parts closely 
contiguous. 
Surface marked by fine lamellose transverse striae, which are slightly 
undulated upon the body of the shell. 
The specimen presents a few slight undulations upon the surface, but is not 
ridged or plicate like the two preceding ones. 
Fig. 11. View of the upper side of the spire, which is incorrectly represented at the apex. 
The apparent contraction toward the anterior side of the aperture is due to acci¬ 
dent. 
Geological position and locality. In the slialy limestone of the Lower Helderberg 
group : Schoharie county. 
Figures 12 a, b , are casts of a species having free volutions, probably of the 
preceding or of P. retrorsum , from the shaly limestone near Catskill. 
[ Paleontology III.] 41 
