A REVISION OF THE SOUTH AMERICAN NEMATOGNATHI. 



The order Nematognathi was established by Dr. Gill 

 in 1870, and characterized by Dr. Cope as follows: 



" Praecoracoid arch present. No coronoid or sym- 

 plectic bones. Parietals and suproccipital confluent; four 

 anterior vertebrae coossified, and with ossicula auditus. 

 No mesopterygium. Basis cranii and pterotic bone sim- 

 ple; third superior pharyrigeal bone wanting, or small 

 and resting on the fourth; second directed backward. 

 One or two pairs of basal branchihyals; two pairs of 

 branchihyals. Suboperculum wanting, premaxillary 

 forming mouth-border above. Interclavicles present." 



As in Diplomystes the maxillary forms the mouth- 

 border above, and the symplecticum is sometimes pres- 

 ent ( fide J. A. Ryder), a revision of this diagnosis is 

 necessary. 



Various views have been held as to the number of 

 families into which the order ought to be divided. 

 Cuvier, Valenciennes and Giiiither have united all the 

 forms under the family name Silurida3. Agassiz was 

 the first to insist, in 1829, that the differences existing 

 between some of the genera were of family value and 

 separated his Goniodontes. 



Bleeker, in 1858, divided the Siluridse of Cuvinr into 

 four, and in 1864 into six families. 



Cope in 1870 recognized three families, and Gill, in 

 1872, gave names to eleven families of Nematogiiathi. 



Without critically examining non-American forms we 

 recognized in 1888 seven families as inhabiting the 

 Americas. 



In 1890, we proposed to raise Diplomystes to family 

 rank.* 



A cursory examination of the skeletons of Asiastic forms leads us to 

 "believe that all the families named by Dr. Gill will probably be found 

 tenable. 



