The body is rather deep; the scales and cranial bones striated; the fins are large, many-rayed; their fulcra small; the dorsal is nearly opposite the interval between the ventrals and the anal; the base of the ventrals is long. The operculum is narrow and pointed below; a small triangular subopercular plate, whose anterior superior angle is produced upwards in a narrow linear process lying along the anterior margin of the operculum for some distance, is intercalated between the last-named bone and the anterior part of the upper margin of the interoperculum. The laniary teeth are sharp, conical, moderate in size, and pretty closely set, with a series of smaller teeth outside.
The peculiar characters of the Amhlypterus striatus of Agassiz render necessary the institution for it of a new genus, which I propose to denominate Cosmoptychius, being in some respects intermediate between Rhabdolepis and Elonichthys, but differing from both in the extended bases of the ventral fins. In the last respect, as well as in the form of some of the bones of the head, it resembles Cheirolepis, though of course differing very widely from that genus in other respects. As yet we are only acquainted with one species of Cosmoptychius, which has been found only in the Lower Carboniferous strata (Calciferous Sandstone series) of the neighbourhood of Edinburgh.
IV. Type of A. nemopterus (Genus Elonichthys, Giebel). The scales are moderate, striated or striato-punctate; the median fins, and sometimes also the paired fins, are large and many-rayed; their fulcra small; the rays of the pectoral articulated; the base of the ventrals not extended; the dorsal situated nearly opposite the interval between the ventrals and the anal; the caudal powerful. The suspensorium is very oblique; there is no subopercular plate intercalcated between the operculum and the interoperculum. There are large conical laniary teeth intermixed with and internal to a series of smaller ones.
To this type belong the A. nemopterus of Agassiz, and one of the two species which he confounded together under the name of A. punctatus (Poiss. Foss. Atlas, vol. ii. tab. 4 c. figs. 3 and 5). Between these and at least two others referred to Palæoniscus by Agassiz, viz. P. striolatus, Ag., and P. Robisoni, Hibbert, it is, as already mentioned, simply impossible to draw any generic distinction. The same must be also said of his "Pygopterus" Bucklandi, which resembles Pygopterus in hardly anything save its large size. Palæoniscus Egertoni, Ag., agrees also very closely, save in the structure of the pectoral fin, in which the principal rays do not commence to be articulated for a little distance from their origin. Of Amhlypterus Portlockii, Egerton, I have only seen fragments; but, so far as these go, they seem to show that this species belongs to the same type with the others named above, as probably also do Palæoniscus Brownii of Jackson and P. peltigerus of Newberry.
As these fishes can be included in none of the three genera already defined, nor yet in Palæoniscus, in the sense in which that generic term must now be employed. it remains to be inquired if they con-
