GREGORY: FISH SKULLS 



195 



Nematognathi (Catfishes) 



In the catfishes (Nematognathi) of the various families, specialization in skull structure 

 goes to far greater lengths than in the characins and carps. In the typical forms the skull- 

 roof (Fig. 11^ is widened out into a sort of cephalic shield to which the broadened supra- 

 orbital, dermosphenotic, sphenotic, pterotic and posttemporal plates contribute. In addi- 

 tion to this, a nuchal shield Is often formed by the expansion and coalescence of the bony 



lot chamber 

 of airbhdc/er 



Ictalurus punctatus 



B Clarias 



Fig. 78. Skulls of catfishes. A. Iclalurus punctatus. B. Clarias sp. C. Relations of the air-bladder to the fourth ver- 

 tebra in a typical nematognath, Ictalurus sp. 



supports of the first three rays of the dorsal fin, together with the posterior process of the 

 supraoccipital. Another sign of high specialization is the apparent loss of the parietals, 

 opisthotic, symplectic and subopercular. The jaws are peculiarly specialized in most 

 siluroids in the reduction of the maxillae to small bones that support the barbels. Diplo- 

 mystes, however, the most primitive catfish, has a well developed maxillary, expanded 



