990 



CLASS PISCES. 



has the dorsal fin placed behind the pelvic ; and in this and several 

 of the other genera the vertebrae consist of the upper and lower 



horse-shoe-shaped elements mentioned 

 in the preliminary notice of the order. 

 Family Leptolepidim:. — Of strik- 

 ing similarity in external contour to 

 the Caturoids is the genus Leptolepis 

 (fig. 929), which is placed by Dr 

 Giinther next to that family, although 

 some palaeontologists regard it as a 

 Teleostean. The vertebral column is 

 fully ossified, and the fins are with- 

 out fulcra. In this genus, which 

 ranges from the Lias to the Kimer- 

 idgian, the dorsal fin is placed im- 



I mediately over the pelvic ; but in 



" Jfe ' : A I Thrissops, of the Kimeridgian, it is 



f A Jm ' above the anal. In external charac- 



ters these Fishes cannot be distin- 

 guished from Teleosteans ; and it is 

 probable that they are intimately 

 connected with that order, even if 

 they should not be placed in it. 



Family Amiid^e. — In the Amioids 

 the vertebral column is fully ossified, 

 and in the caudal region has a series 

 of centra bearing the neural and 

 haemal arches, which alternate with 

 intercentra devoid of such append- 

 ages. Fulcra may or not be pres- 

 ent ; and the caudal fin is convex, 

 with the extremity of the vertebral 

 column bent sharply up into the 

 upper lobe. In Mega/urus, of the 

 Purbeck and Kimeridgian, fulcra are 

 present, and the dorsal fin is short, 

 and does not extend in advance of 

 the pelvic. Lophiurus, from the 

 same horizon, and Opsigonus and Amiopsis, of the Lower Chalk, 

 are other genera, of which the first two are nearly related to 

 Megalurus. The existing Amia, of the freshwaters of the southern 

 United States, has no fulcra, and the dorsal fin occupies three- 

 quarters of the length of the body. It appears probable that this 

 genus is represented in the Upper Eocene (Lower Oligocene) and 

 the Lower Miocene of the Continent, where its remains have been 



Fig. 928 bis. — Skeleton of Caturus 

 elongatus ,' from the Kimeridgian of 

 France. One-half natural size. (After 

 Zittel.) 



