FOSSIL FISHES. 25 
P. latus J. A. R, P. macropterus W. C.R, P. Agassizii W C. R., and P. ovatus 
W.C.R. Mr. Redfield in this article pointed out some of the peculiarities of 
this group of fishes, and suggested that they should perhaps be separated 
from Palaoniscus. 
This was subsequently done by Sir Philip Egerton,’ who, on account of 
the great strength of the fin rays, named the genus which he created to 
receive them Jschypterus. Unfortunately no detailed description of the 
anatomical characters of the genus was given by Sir Philip Egerton, as 
he scarcely had sufficient material for the purpose. This is much to be 
regretted, as with his great knowledge, if he could have made a careful study 
of good specimens, he would have been led to discover and report the true 
relationship of the group. This is plainly with Lepidotus and its allies, and 
not with Palwoniscus, as supposed by Agassiz; an error into which he was 
led by the imperfect preservation of the fishes he examined, none of which 
showed any details of the all-important structure of the head. The head 
was small, and all the bones were delicate; hence the almost universal de- 
ficiences in this part of their structure when fossilized. Among the many 
hundred specimens of Ischypterus I have passed in review I have found a 
few in which nearly all the details of the bony structure were preserved, 
and I am able to describe this more fully than has before been possible, and 
to deduce from it with certainty the zoological relations of this group of fishes. 
Where distinctly visible the structure demonstrates an intimate relationship 
with Lepidotus, Dapedius, and Pholidophorus, but most of all with Semionotus. 
Here the affinity is so close, that it is probable that both Agassiz and Sir 
Philip Egerton would have united schypterus with that genus if the material 
at their command had been more abundant and better. In an examination 
of nearly all the specimens of Ischypterus contained in the museums of the 
United States and a considerable number of individuals of Semionotus I have 
been unable to detect any characters by which they can be distinguished. 
The outlines, size, and proportions of the body are essentially alike ; both are 
elliptical or ovoid, with a relatively small, pointed head, and weak, scarcely 
lobate tail. The positions, form, and structure of the fins are so nearly alike 
that the differences can hardly be regarded as of more than specific value. 
' Quart. Jour, Geol, Soe. London, vol. 6, 1850, p. 8. 
