360 FISHES. 



Third Family — Phaneropleupjd.^. 



Caudal fin difliycercal ; vertical fin continuous. Gular 

 plates. Scales cycloid. Jaws ivith a series of mimite conical 

 teeth on the margin. 



Extinct. Phaneropleuron from Devonian formations, and 

 the carboniferous Uroncmus are probably generically identical, 



FOURTH SUB-ORDER— CHONDEOSTEI. 



Skeleton notochordal ; skull cartilaginous, with dermal 

 ossifications ; hranchiostegals few in number or absent. Teeth 

 minute or absent. Integuments naked or ivith bucklers. Caudal 

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



First Family — Acipenserid.^]:. 



Body elongate, sub-cylindrical, vAtli. five rows of osseous 

 hecklers. Snout 2^'>'odifced, suhspatidate or conical, with the 

 mouth at its lower surface, small, transverse, protractile, tooth- 

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

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

 Dorsal and anal fins approximate to the caudcd. 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 ivall of 

 the oesophagus. 





Fig. 142. — Tail of Acipenser. «, Fulcra; h, osseous bucklers. 



