PISCES. 239 
paleontologist. The family of Cephalaspides exhibited features so bizarre, 
as to cause them to be placed anywhere else than among fishes: it was 
Agassiz who first, recognised their true character, and placed them in the 
position to which they properly belong. The essential character is to be 
found in the broad, tesselated, bony plates, which encircle the head and a 
part of the trunk. The form, number, and arrangement of these, vary 
ereatly in the different genera, although they possess one general character 
in the enamel coating, the smooth inner face, and the variously marked or 
oranulated exterior. The head is covered by a simple or compound, 
always flat, buckler, of various characters. The body, like the head, is 
flat, and variously covered with plates. The fins exhibit a peculiar 
development, the ventrals are entirely absent, the pectorals of a narrow 
rayless plate, situated behind the head, produced more or less into a wing. 
With a single exception, the caudal fin is entirely wanting, and the dorsal 
and anal, when developed, never attain to any considerable size. In the 
structure of the skeleton they exhibit some close affinities to the sturgeons. 
No species have as yet been found in North America. 
The concluding family of the Chondrostei, HoLorrycuu, is composed of 
fishes with slender and powerful bodies, thick heads, wide jaws, and well 
developed fins. The jaws are furnished with small, sharp teeth, at the 
edge, and with a few others that are very large, strongly conical, at 
considerable distances apart; these, with the fins, indicate a highly 
predacious character. All the teeth are covered with vertical folds, which 
become lost towards the apex. The scales, in form and arrangement, 
resemble those of the true cycloids, and overlap each other in oblique 
series. Their coating of enamel, however, indicates clearly their ganoid 
structure. Even the bones of the head are covered with enamel, and 
variously sculptured on the surface. The fin rays and bones, as far as 
these exist, possess Internal cavities, an unique character peculiar to these 
fish. The genera belong to the old red sandstone and the Devonian, but it 
is doubtful whether any species, either of this family or of the preceding, 
occur in North America. The reported occurrence of Holoptychius 
nobilissimus in Pennsylvania and New York wants confirmation. 
Before commencing the consideration of the truly cartilaginous fishes 
forming the division Selachii, as distinguished from the Teleostet and 
Ganoidet, it will be necessary to dwell for a moment upon the ninth order 
of the tabular classification placed at the head of our article, and 
constituted by a single family, the Srrenorper. This family includes two 
species, of, perhaps, two different genera, the Lepidosiren paradoxa from 
Brazil, and Lepidosiren, perhaps Protopterus annectens, from the Gambia 
River, Africa. By most Continental naturalists the Lepidosiren is 
considered to be a reptile, while Professor Owen is confident as to its 
ichthyal character. It in fact combines the characters of both reptile and 
fish, to a most remarkable degree, the African species inclining more to the 
latter, the South American to the former. Deferring further consideration 
of the subject until we come to the class of Reptiles, we proceed to the 
subject of the Selachii, above referred to. 
443 
