PISCES. 237 



give to the skin an appera'ance 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 af 

 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. 



In the Heterocerci monopterygii, 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 

 fulcra on the fin borders are almost always present. It is in this family that 

 most of the American Holostei are included. In the genus Euri/notus, 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. 

 Eurynotus tenuiceps, from the new red sandstone of Sunderland, Mass., 

 and Middletown, Conn., and E. jiinhrialus, from New Haven, are the 

 American species. 



The extensive genus Palceoniscus 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 si^e, but 

 always have a rhomboidal outline. The pectorals and ventrals are not 

 much developed, the short anal more so, and still moi'e the long rayed 

 dorsal. The caudal is deeply cleft, and perfectly heterocercal. The 

 American species are : Palceoniscus fiiltus, 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 

 Amhlypterus, with some affinities with Palceoniscus, 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 



441 



