﻿Miss Agnes Crane — On Certain Living and Fossil Fishes. 213 



flouts, and then the link is lost sight of until their lineal descendants 

 reappear widely distributed on the surface of the present world. 

 This is but an illustration of the truth that species whicb have the 

 greatest vertical range in time have also the widest geographical 

 distribution, or that a wide distribution proves the antiquity of tlie 

 genus. It is certainly a very significant fact that the group of living 

 fish most closely allied to the amphibian reptiles should be repre- 

 sented in the Devonian rocks, long before the most simply con- 

 structed amphibians appeared on the scene of life in the swamps of 

 the Carboniferous period. The Dipnoi, as at present constituted, 

 includes the following families : Frotopterina, Ceratodontina, Cteno- 

 dodipterid(B, and possibly Phaneropleuridce. They are closely allied 

 to the G-anoids, and especially to that sub-order termed, by Prof. 

 Huxley, the Crossopterygidce, or " fringe-finned," to be presently re- 

 ferred to. Dr. Giinther, indeed, proposes to unite the dipnoids with, 

 the ganoids, as a distinct family ; but Prof. Huxley considers that, 

 though nearly related to that order, they yet possess many important 

 differences. It seems as if the Dipnoi had also some affinities with 

 the group of fishes known as Placoderms, for a most remarkable 

 fossil fish has recently been discovered in America, the dentition of 

 which is almost exactly like that of Lepidosiren, except that it is 

 about one hundred times greater. The genus DinicJithys was founded 

 by Prof. Newberry for the reception of this gigantic Placoderm, of 

 which two species at least are recognized and graphically described 

 by him, in vol. ii. of the State Eeports of the Paleeontology of Ohio. 

 They occur in the Huron Shales of the Upper Devonian series, 

 where they seem to have preponderated in number, fragments of 

 over a hundred individuals having been detected, while the remains 

 of other genera are found more rarely in the same horizon. The 

 jaws of this "terrible fish " were each two feet long, the breadth of 

 the head was about three feet, and the cranium was composed of 

 massive bony plates, the solid bone of the occipital portion being 

 three inches in thickness. The length uf the body is estimated by 

 Professor Newberry to have been about fifteen feet, and its diameter 

 three. The anterior portion was protected by huge dorsal and 

 ventral shields, resembling, in general shape and structui-e, those 

 of the genus Coccosteus, rendered classic by the pen of Hugh 

 Miller. Very little is known with regard to the fins, " about six 

 inches only of an apparently median fin, with well-ossified rays as 

 thick as one's little finger," having as yet been found, and, from the 

 absence of scales, it is conjectured that the posterior portion of the 

 body of the animal was covered with a tough skin, as in Coccosteus, 

 a genus which possibly protected itself, like the modei^n sheat fish 

 of the Gauges, by bun-owing in the mud, watching for prey with 

 only its mail-clad parts exposed. The powerful dentition of Dinich- 

 thys is suggestive of carnivorous habits, and probably being so heavily 

 weighted by the thick shields encasing its vital organs it would be 

 compelled to obtain food rather by cunning than by swift pursuit. It 

 is worthy of notice that the ponderousl}^ armed Placoderms had a com- 

 paratively short range in time, remains of the group being only found 



