478 E. N.S. Ringueberg—Dinicthys from New York. 
Anterior margin describing an almost perfect semicircle of 
five and one-half inches in diameter, which comprises the 
anterior five ninths of the plate, and represents its widest 
extension; a slight sinus half way from the crest on either 
side. The highest point of the shield is on a ridge situated a 
little back from the anterior median margin and extends at 
right angles across the upper part, from which elevation the 
surface is beveled off toward the outer margin. 
Posterior portion rather squarish, strongly sinuate ; the two 
lateral sinuses sharply cut out nearest the forward part, where 
they end with a well defined angle at their junction with the 
anterior semicircular portion; posteriorly, curving around the 
sub-obtuse latero- anterior angles into the lateral posterior 
sinuses. Posterior margin with a wide shallow median sinus, 
and two smaller lateral ones. 
The latero-posterior angles are placed on a line with the cen- 
tral portion of the median sinus, and the shield is one-half inch 
narrower here than at the median transverse diameter. A 
slight median Sse ebaciaest depression along the central portion 
hi 
lateral sinus in the specimen figured is slightly deeper than the 
left. It must have been of large size, though but a pigmy 
compared with its congeners of the adjacent seas, some of which 
were from two to three feet across their armor-clad backs. 
