142 PALEONTOLOGY OF NEW JERSEY. 
strong, coarse, rounded, vertical ridges; very irregular and uneven in 
size, and with deep constrictions between. The ribs are frequently bifur- 
sated, and not uncommonly one may be seen to divide and form a cluster 
of six or seven at the base in large specimens. The rostrum plate is pro- 
portionally large and the rostro-lateral also, while the carina and carino- 
laterals are small and narrow, although longer than the others; but the 
number of ribs on each is so variable that it is not possible to say what the 
prevailing number on any plate would be. The al and radii are very nar- 
row, the latter often obsolete on the carinai plates, as far as seen on the 
exterior of the body. This causes the shells after death to separate and fall 
asunder with little movement. Hence the separated plates in the New Jer- 
sey deposits. ‘The transverse striae or wrinkles, mentioned in the description, 
are widely separate, very prominent, although very fine and thread-like, and 
are readily seen under a glass. 
Formation and locality: The specimens used come to me from near 
Shiloh, N. J., and are from the collection at Rutgers College. 
