360 FISHES. 



Third Family — Phaneropleueid^. 



Caudal jm diphycercal ; vertical fin continuous. Gular 

 plates. Scales cycloid. Jaws with a series of minute conical 

 teeth on the margin. 



Extinct. Phaneropleuron from Devonian formations, and 

 the carboniferous Uronemus are probably generically identical. 



FOURTH SUB-OEDER— CHONDEOSTEI. 



Sheleton notochordal ; skull cartilaginous, with dermal 

 ossifications ; branchiostegals few in number or absent. Teeth 

 minute or absent. Integuments 'iia'ked or with bucklers. Caudal 

 fin heterocercal, with fulcra. Nostrils double, in front of the eyes. 



First Family — ^Acipenseeid^. 



Body elongate, sub-cylindrical, with five rows of osseous 

 bucklers. Snout produced, subspatulate or conical, with the 

 mouth at its lower surface, small, transve^^se, protractile, tooth- 

 less. Four barbels in a transverse series on the lower side of the 

 snout. Vertical fins with a single series of fulcra in front. 

 Dorsal and anal fins approximate to the caudal. Gill- 

 membranes confluent at the throat and attached to the isthmus. 

 Branchiostegals none. Gills four ; two accessory gills. Air- 

 bladder large, simple, communicating with the dorsal wall of 

 the msophagus. 



Fig. 142. — Tail of Acipenser. a, Fulcra ; b, osseous bucklers. 



