Miss Agnes Grane — On Certain Living and Fossil Fishes. 213 
donts, 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 which have the 
greatest vertical ränge in time have also the widest geographical 
distribution, or that a wide distribution proves the antiquity of the 
genus. It is certainly a very significant fact that the group of living 
fish raost 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 : Protopterina, Ceratodontina, Cteno- 
dodipteridce, and possibly Phaneropleuridce. They are closely allied 
to the Ganoids, and especially to that sub-order termed, by Prof. 
Huxley, the Crossopterygidce, or “ fringe-finned,” to be presently re- 
ferred to. Dr. Günther, indeed, proposes to unite the dipnoids with 
the ganoids, as a distinct family ; bat 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 Dinichthys 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 Reports of the Palaeontology 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 of 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 structure, those 
of the genus Coccosteus, rendered classic by the pen of Hugh 
Miller. Yery little is known with regard to the fins, “ about six 
inches only of au 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 modern sheat fish 
of the Ganges, by burrowing 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 ponderously armed Placoderms had a com- 
paratively short ränge in time, remains of the group being only found 
