68 TRIASSIC FISHES AND PLANTS. 
terus, viz, relatively large spinous fulera border the margins, the rays are 
few and widely separated, the caudal is narrower than in most species of 
Ischypterus, and the inequality of the extremity of the body—i. e., the heter- 
ocercy—is about the same as in Ischypterus, and considerably more marked 
than in Catopterus. 
Searching for allies of these little fishes among the figures and descrip- 
tions which have been published I find in Agassiz’s Palwoniscus glaphyrus 
and in the three fishes described by J. W. Kirkby,’ and called by him 
Paleoniscus altus, P. Abbsii, and P. varians, what perhaps may be members 
of the same genus. More material, and that in a better state of preserva- 
tion will be required, however, before a satisfactory comparison can be 
made. It is perhaps not certain that the group referred to all belong to 
one genus. For example, Puleoniscus altus of Kirkby very closely resem- 
bles our small ovoid species of Ischpyterus CL. latus), differing, so far as I can 
see, only in this, that none of the median row of dorsal seales in P. altus 
are spiny. Dr. R. H. Traquair—who has made a careful study of the 
fishes described. by Mr. Kirkby—considers this a character of generic 
value, and it has led him to place all the group of Ischpyterus-like fishes 
(Paleoniscus glaphyrus, P.altus, P. varians, and P, Abbsii) mm a new genus, 
which, from the absence of spiny scales, he calls Acentrophorus.* 
In the Chicopee fishes the structure, so far as can be made out, is 
altogether that of Ischypterus, except that the median dorsal seales are all 
rounded or ovoid. Unfortunately the details of the head structure are ob- 
secured by the metamorphosis to which the inclosing rocks have been sub- 
jected. The teeth are, however, distinctly shown, and they prove to be 
conical, pointed, and relatively strong. The form of the body is more 
elongated than in most species of Ischypterus; in that respect resembling 
Kirkby’s Palwoniscus varians and P. Abbsii, but the dorsal fin is placed 
farther back than in those fishes or in any species of Ischypterus known. 
It is, in fact, but little in advance of the anal. All the fins, including the 
caudal, have the structure of those of Ischypterus, having few and many- 
jointed rays and long spiny fulera, but all are relatively weak. 
1 Quart. Jour. Geol. Soc. London, vol. 20, 1864, p. 353. 
2 Quart. Jour. Geol. Soc. London, vol. 33, 1877, p. 560. 
