280 
Proceedings of the Royal Society 
own collection, which belong to a species perfectly distinct, even 
generically, from the first. The presence in the jaws of this species of 
sharp conical teeth of different sizes, as well as its entire aspect, shows 
that it is referable to the same genus as Elonichthys striolatus , 
(. Palceoniscus striolatus, Agassiz) with which it is indeed closely allied. 
Description . — The largest specimen in my collection measures6 £ 
inches in length, but, as it is a little contorted laterally, it must have 
been originally somewhat longer; the more ordinary length is from 5J 
to 6J inches. The form of the body is fusiform, but as hardly any 
specimen is absolutely free from some amount of distortion, it is 
difficult to ascertain the proportional measurements with absolute 
accuracy; two very good examples, however, agree in this, that 
the length of the head is contained a little more than four times, 
and the greatest depth of the body (just in front of the dorsal fin) 
a little more than three times in the total length, up to the bifurca- 
tion of the caudal fin. 
Many of the details of the structure of the head are clearly 
shown. The outer surfaces of the bones of the cranial shield dis- 
play a fine tubercular ornamentation, the tubercles frequently 
passing into short rugae; the superethmoidal forms as usual a 
blunt prominence projecting over the front of the mouth. The 
suspensorium is very oblique, and the gape consequently of great 
extent. The operculum is rather narrow, its posterior-superior angle 
is rounded off, the posterior-inferior one acutely pointed, its outer 
surface is marked with delicate and somewhat distant ridges, 
which mostly follow the direction of the lines of growth. The 
interoperculum is square-shaped and apparently similarly orna- 
mented, though it is difficult to obtain a satisfactory view of its 
external surface. The exact number of the branchiostegal rays is 
hardly ascertainable ; in many specimens the anterior one of each 
lateral series is distinctly shown to be much broader than the rest, 
and a median lozenge-shaped plate is also conspicuously present 
between these, and behind the symphysis of the mandible. The 
maxilla is of the usual form ; its broad portion is ornamented with 
delicate raised striae placed rather widely apart, and mostly parallel 
with the superior and posterior margins; they are closer and more 
pronounced along the dentary margin. The mandible is moder- 
ately stout, and closely striated externally with delicate ridges, 
