90 



PISCES 



CLASS I 



overlap. Notwithstanding their thinness, however, the scales exhibit the 

 characteristic structure of true ganoid scales ; the base contains bone cells, the 

 surface is covered with enamel. In many Jurassic genera the vertebral 

 column consists of hem i- vertebrae or complete rings, but it is also often 

 completely ossified. Contrary to the arrangement in certain closely related 

 bony fishes (Physostomi), the terminal vertebrae are continued some distance 

 into the upper lobe of the tail. 



Only one genus (Amia) still survives in the rivers of the southern United 

 States and Central America. The order ranges upwards from the Upper Lias. 



Fig. 162. 



Family 1. Pachycormidae. Doderlem. 

 (Microlepidoti and Cyclolepidoti, Zittel.) 



Vertebral axis with very numerous segments, with or without hemi- vertebrae. 

 Ethmoid forming a prominent rostrum. Branchiostegal rays very numerous (thirty 



to forty). Neural spines in abdominal 

 region separate from arches. Caudal fin 

 deeply forked, powerful, only infernally 

 heterocercal. Teeth laterally compressed, 

 lanciform, in two series, the largest of which 

 are set in alveoli, Upper Lias to Upper 

 Cretaceous. 



Pachycormus, Ag. Large, salmon- 

 shaped fishes, with hemi-vertebrae only 

 Euthy't micropodius, Ag.sp. Upper i in t ^ e cau d a l reeion. Operculum, sub- 



Wurtemberg. A, Vertebrae (c, Haemal arches; hyc, o r 



Hypocentrum ; n, Neural arches ; p, Parapophyses ; operculum, and Suborbitals Vdy large. 



pic, Pleurocentrum ; sp .Neural spine). B, Scales. -.^T P ,, ., n -^.i j- 



Rays of all the fins with distant 

 articulations. Pectoral fins large ; pelvic fins absent ; short dorsal fin arising 

 in front of the anal ; deeply 



forked caudal with elongated 7 nj N f / y y j j jj /^ 



fulcra on each lobe. P. 

 macropterns, Blv. sp., and 

 other species in the Upper 

 Lias of Germany, France, 

 and England. 



Euthynotus, Wagner 

 (Heterothrissops, Pseudo- 

 thrissops, Sauvage), (Fig. 

 162). Hemi-vertebrae pre- 

 sent. Fin fulcra minute. 

 Pelvic fins present ; dorsal 

 fin opposed to much ex- 

 tended anal fin. Scales 

 rhombic, rounded at the 

 angles. E. speciosus, Wagn., 

 and other species in the 

 Upper Lias of Germany and 

 France. 



Hyp s o corm u s, W a g n e r 

 (Fig. 163). Large fishes, with very small rhombic scales, much resembling 





IMP* 



Fig. 163. 



Hypsocormus insignis, Wagn. Portion of trunk. Upper Jurassic 

 (Lithographic Stone) ; Eichstadt, Bavaria. 



