PISCES. 237 
give to the skin an appearance like shagreen. Under the lens they 
seem to be of a rhomboidal form, with the characteristic enamel. The 
body is generally fusiform, compressed. The head large and_ broad, 
the jaws broad, and armed with conical teeth, and opening widely. 
The family is represented, in North America, by a single species of 
Acanthodes. The genus is recognised by the projecting lower jaw, 
the’ absence of an anterior dorsal, the small caudal, and the very 
minute scales. The small ventrals lie close together in the middle line 
of the body and in the middle line of the belly, and the dorsal 
stands opposite to the somewhat larger anal. The species Acanthodes 
sulcatus, from the carboniferous of New Haven, has regularly rhom- 
boidal scales, with an arched enamelling, and vertically diagonal broad 
furrows. 
Tu the Herrerocerct monopreryer, the larger scales, and the absence 
of a strong spine in the lateral fins, form the distinctive feature in 
respect to the preceding family; and the single dorsal separates it 
from the one before that. The positive characters of the family are 
very variable; the teeth, however, are generally small and acutely 
conical, rarely obtuse. The rhomboidal scales are never imbricated. The 
fulera on the fin borders are almost always present. It is in this family that 
most of the American Holostei are included. In the genus Eurynotus, the 
dorsal extending over nearly the whole back, with its elongated first ray, is 
situated anterior to the anal; the body is rather slender; the pectorals are 
greatly elongated, the ventrals moderate. The head is rather small, the 
jaws armed with very minute obtuse teeth, the scales of medium size. 
“Hurynotus tenuiceps, from the new red sandstone of Sunderland, Mass., 
and Middletown, Conn., and E. fimbriatus, from New Haven, are the 
‘American species. 
The extensive genus Palgoniscus embraces fish of moderate size, with 
fins of no great development. The body is elongated, or slender, or com- 
pact. The head is small and rounded; the mouth deeply cleft, the jaws 
well supplied with small card teeth; the operculum large and broad, the 
preoperculum strongly curved. The scales vary in form and size, but 
always have a rhomboidal outline. The pectorals and ventrals are not 
much developed, the short anal more so, and still more the long rayed 
dorsal. The caudal is deeply cleft, and perfectly heterocercal. The 
American species are: Palgoniscus fultus, from Sunderland, Mass., Durham 
and Middletown, Conn., Pompton and Boonton, New Jersey. P. carinatus, 
New Haven, P. agassizii and P. ovatus, Middletown, Durham, and West- 
field, Conn. ; Sunderland, Mass. ; Boonton and Pompton, N.J. P. macro- 
pterus, Sunderland, Middletown, Durham, and Boonton. The genus 
Amblypterus, with some affinities with Paleoniscus, exhibits a greater 
development of fins, and a longer and broader body. The fin rays are thin, 
short jointed, and split only at the end. The ventrals are anterior to the 
middle of the body, the dorsal in the middle, the extended anal only a little 
behind it. The moderate scales are rhomboidal, smooth, or furrowed. The 
head is provided with large orbits and opercular pieces, the powerful jaws 
44] 
