FOSSIL FISHES. 67 
more vertebrated tail. From P. curtus Egerton it differs in its more elon- 
gated form, in the plication of the scales, and the more heterocereal tail. 
The discovery in our Triassic rocks of a species of Ptycholepis, a genus 
before found only in the Lias of Europe, might seem to open up again the 
long-debated question of the age of the New Red Sandstone of the Atlantic 
_ States, but in fact it does not seriously invalidate the conclusion, based on 
other evidence, that this series of strata is the equivalent of the Rheetie beds 
of Europe. The fish now described is a new species, and has the vertebral 
column prolonged to a greater distance into the upper lobe of the tail than 
its Liassic representatives. Without attaching too much importance to this 
character, we may fairly infer that it indicates a little earlier date. 
The two specimens now figured are perhaps about the average in size 
of all those yet found, but I have one which is eight inches long by two 
inches wide; another specimen is only four inches long by five-eighths of 
an inch wide. As a whole our specimens are much smaller than the average 
of those of P. Bollensis. P. curtus, of Egerton, from the Lias of England, 
is no longer than our specimens, but it is much more robust. 
I have dedicated this species to Prof. O. C. Marsh, of Yale College. 
All the specimens yet known have been obtained by S. W. Loper, at Dur- 
ham, Conn. 
Genus ACENTROPHORUS Traquair. 
From the Triassic rocks at Chicopee Falls, Mass., a considerable num- 
- ber of little fishes have been obtained which are distinctly different from 
any others found in this country. Their affinities with Ischypterus are so 
close, that I was for a long time disposed to consider them as belonging to 
a species of that genus. The structure is essentially the same throughout, 
with the exception that the crest of spinous scales which crowns the dorsal 
arch in Ischpyterus is here wanting and the median line is marked by a 
series of round or oval scales a little larger than the quadrangular ones 
which accompany them on either side. The body is fusiform or conical, 
widest near the head, tapering gradually with nearly straight lines above 
and below; the fins are all weak, the dorsal placed far back, nearly as far, 
indeed, as in Catopterus. ‘The structure of the fin is like that of [schyp- 
