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 hemi-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 (Amin) still survives in the rivers of the southern United 

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



Family 1. Pachycormidae, Dödeiiein. 

 {Microlepidoti and Cf/clolepidoti, Zittel.) 



Vertebral axis with very numerous segments, with m' ivithout hemi-vertebrae. 



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



^ j, to forty). Neural spines in abdominal 



vi<\ sp region separate from arches. Caudal fin 



^-(^^ ^^^^ ^- j^^. deeply forked, poweiful, only internally 



heterocercal. Teeth laterally compressed, 



^y^ IL^y '"lä^^ JS^MB^ß^ lanciform, in two series, the largest of which 



are set in alveoli. Upper Lias to Upper 

 Cretaceous. 



Pachycor7Hus, Ag. Large, salmon- 



Fia. 162. 



Kuthynotm micropodiufi, Ag. sp. Upper Lias ; Boll. 

 Würteraberg. A, Vertebrae (o, Haeinal arclies ; hyc, 

 Hypocentrum ; n, Neural arches ; p, Parapophyses 

 plc, Pleurocentrum ; sp, Neural spine). B, Scales. 



articulations. Pectoral fins large 

 in front of the anal ; deeply 

 forked caudal withelongated 

 fulcra on each lobe. P. 

 macropterus, Blv. sp., and 

 other species in the Upper 

 Lias of Germany, France, 

 and England. 



Euthynotus, Wagner 

 (Heterothrissops, Fseudo- 

 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. 



Hypsocormus, AVagner 

 (Fig. 163). Large fishes, with very small 



shaped fishes, with hemi-vertebrae only 

 in the caudal region. Operculum, sub- 

 operculum, and suborbitals very large. 

 Rays of all the fins with distant 

 pelvic fins absent ; short dorsal fin arising 



i'Ki. 



Hypsocormus insignis, Wagn. Portion of trunk. Upper Jurassic 

 (Lithographie Stone) ; Eichstädt, Bavaria. 



•hombic scales, much resembling 



