Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/655

Rh form of the anal fin and the structure of the pectoral. In Pygopterus the dorsal is placed nearly opposite the commencement of the anal, commencing only a little in advance of the latter, which is possessed of a remarkably extensive base, being produced posteriorly in a fringe-like manner; the principal rays of the pectoral are also unarticulated till towards their terminations. It is true that in E. Egertoni and one or two other species still undescribed, these rays are not articulated to the same extent as in E. nemopterus, &c.; but I feel rather reluctant, on that ground alone, to multiply the number of genera.

V. Type of A. punctatus, pars (Genus Gonatodus, Traquair). Under the name of "Amblypterus punctatus" three imperfect specimens of fish from the shales of Wardie, near Edinburgh, were figured by Agassiz in the 'Poissons Fossiles.' One of these is a head with the anterior part of the body (Atlas, vol. ii. pi. 4 c. fig. 4); the second (ibid. fig. 5) wants the head, shoulders, and extremity of the tail; the third (ibid. fig. 3) displays the entire caudal fin, but is obliquely cut off just in front of the dorsal and anal. But a comparison of these specimens with an extensive series of entire fishes from the same beds establishes the fact that the Amblypterus punctatus of Agassiz was founded upon fragments of two distinct fishes, the specimen showing the head, but without the hinder part of the body, being not only specifically, but even generically, distinct from the other two, in which we have the hinder part of the body without the head. The latter belong to the genus Elonichthys and to a species closely allied to E. striolatus and E. nemopterus, which I propose to call E. intermedius; but for the former the peculiarity of the dentition requires the institution of a new genus, for which I propose the name Gonatodus, retaining for the type species the original term "punctatus." For although the enlarged representations of scales given by Agassiz (tab. cit. figs. 6–8) are taken from one of the specimens referable to Elonichthys, yet the name is indeed applicable to both species; and as the characters of the head and teeth are those which specially distinguish Amblypterus punctatus, according to Agassiz's conception, from his A. nemopterus, with which he contrasted it as occurring in the same beds, it is, I think, more appropriate to retain his specific name for the fish of which those peculiarities are characteristic.

The peculiar dentition of Gonatodus was first correctly described by Mr. R. Walker in a fish from the shales of Pitcorthie, Fifeshire, to which he gave the name of Amblypterus anconoæchmodus, a species which is evidently most closely allied to the G. punctatus of Wardie, and possibly identical with it. I have, however, enjoyed no opportunity of comparing with the latter any actual specimens of the Pitcorthie fish.

The teeth of G. punctatus are from $1⁄20$ to $1⁄24$ inch in length in specimens measuring from 5 to 6 inches: their form is cylindrical, but