ORDER GANOIDEI. 



987 



gnathus ranging from the Keuper to the Kimeridgian, while in the 

 Lias we find Platysiagum and Ptycholepis, and Pholidopleurus and 

 Peltopkurus in the Keuper. A second group is represented by 

 Pleuropholis, of the Kimeridgian of Bavaria, and also by Tho7'aco- 

 pterus and Pterygopterus of the Keuper, the latter being distinguished 

 by the absence of the pelvic fins. The genus Pholidophorus in- 

 cludes small Fishes somewhat resembling a Carp in form, which 

 range from the Muschelkalk to the Purbeck. A fish from the 

 Muschelkalk, originally described as Pholidophorus po?-ro, has been 

 made the type of the genus Prohaleates, on account of peculiar 

 features in its squamation. Larger forms are ranked under the 

 genera Isopholis of the Lias and Kimeridgian, and Ophiopsis, which 

 extends from the Lias to the Purbeck. Of the remaining genera 

 we have Ensemius and Propterus in the Kimeridgian of Bavaria ; 

 JVotagogus from the latter deposits, and also in the Lower Greensand 

 of Italy ; Histionotus in the Bavarian Kimeridgian and the English 

 Purbeck ; Macrosemius ranging from the Stonesfield Slate to the 

 Kimeridgian of Bavaria ; and Legnonotus from the English Lias. 

 Lophiostomus, from the Chalk of Sussex, may perhaps be placed 

 here, although its skull approximates to that of Amia. The scales 

 are pitted, and have a pectinated posterior border. 



Family Aspidorhynchid^: (Rhynchodontid^). — In this family 

 the body is much elongated, and covered with scales of unequal 



Fig. 927.— a, The Gar-pike {Lepidosteus osseus). Recent. North America. B, Aspido- 

 rhynchus; from the Jurassic. Both much reduced. 



sizes ; the skull is produced into a short rostrum ; the caudal fin is of 

 the masked heterocercal type ; the fins carry fulcra ; the vertebrae 

 have ossified rings ; and the teeth are either blunt or sharp. This 

 family is represented only by the Mesozoic genera Aspidorhynchus 

 and Belono stomas, in both of which the dorsal fin is placed above 

 the anal. In the former (fig. 927, b), which ranges from the Lias to 



