422 FOSSIL FISH. 



olite has undergone ; and we may remark here, that in ichthy- 

 olites generally, the traces of the ventral fins are rarely to be 

 found. 



Z. rhomheus, De Blain. This is the Scomber rhombeus of 

 Volta, which in reality belongs to this group. It is a fish re- 

 markable for its breadth, which is almost equal to its length, 

 owing to the great projection of the belly, which considerably 

 exceeds that of the back ; the dorsal fin appears to have been 

 divided into two parts, the anterior of which is somewhat high, 

 and formed of a great number of simple rays ; and the poste- 

 rior, much lower, is equally composed of very small rays, pro- 

 ducing a fan-like form ; the anal fin, much longer than this 

 second part, in consequence of the great curve of the belly, 

 has in other respects the same form and composition ; the pec- 

 torals are very short ; the ventral fins are composed each of a 

 single ray, almost cylindrical, and much longer than the body. 



MoNOPTERUs. Monopterus gigas, Volta. This genus is 

 established on rather a defaced ichthyolite, about a foot long 

 and one half broad : the head is high, rather short, and has a 

 truncated appearance ; the back is extremely gibbous, and 

 covered with some traces of small scales ; there is no indica- 

 tion of eyes, of gill-covers, or even of pectoral or ventral fins, 

 but solely a dorsal fin, pretty far back, rounded, of moderate 

 size, and apparently formed of rays entirely soft; the anal is 

 formed in the same way, but differs in being notched a httle 

 behind, the first rays being much longer than the others ; the 

 caudal, at the end of a pretty long and conical pedicle, is 

 remarkable for its length, the narrowness of its lobes, and the 

 depth of its emargination. 



Pleuronectes. Pleuronectes platessa, Volta. Pleuronedes 

 quadratulus, lb. Both belong to one species : the fossil skele- 

 ton in the first figure is far from complete, especially in the 

 anterior part, where the summit of the head is wanting. The 

 second is much better, and to a certain extent the quadratulus 

 of Belon may be recognized in it. 



