96 CONTKIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 



way the Isospondylous fislies are nearest tlie Halecomorphl, and have 

 probably descended from some Crossopterygian, near the Haplistia, 

 through that order. The affinity of the cat-fishes to the sturgeons is 

 seen in the absence of symplectic, the rudimental maxillary bone, and, 

 as observed by Parker, in the interclavicles. There is a superficial 

 resemblance in the dermal bones." {Cope. 1. c, 454.) 



This group comprises the Siluridcc and their relatives, now divided 

 into several families by Professor Gill. (v^/Jia, thread ; yvdOoq^ jaw j from 

 the maxillary barbels, which are always present.) 



ANALYSIS OF THE FAMILIES OF NEMATOGNATHI. 



* Operculum present ; dorsal fin, if present, short, anteriorly placed. . . Silurid^e, 29. 



Family XXIX.— SILURIDiE. 



{The Vat-fishes.) 



Body more or less elongate, naked or covered with bony plates. 

 !N"o true scales. Anterior part of head witli two or more barbels, the 

 base of the longest pair formed by the rudimentary maxillary. Margin 

 of upper jaw formed by premaxillaries only. Suboperculum absent ; 

 operculum present. Dorsal fin usually present, short, above or in front 

 of the ventrals. An adipose fin usually present. Anterior rays of dor- 

 sal and pectorals usually spinous. Air-bladder usually present, large, 

 and connected with tL e organ of hearing by means of the auditory ossi- 

 cles. Lower pharyngeals separate. 



After the removal of numerous aberrant forms as distinct families, 

 the family of Siluridcc, as understood by Professor Gill, contains more 

 than 100 genera and upward of 900 species. Most of the Siluridce are 

 fresh-water fishes, inhabiting the rivers of warm regions, particularly 

 South America and Africa. Comparatively few of them are marine, and 

 these few are mostlj^ tropical. 



Our species all belong to the division called by Dr. Giinther, Siluridce 

 Proteroptercc, and thus characterized : 



" The rayed dorsal is always present, short, with not more than 12 

 soft rays, and belongs to the abdominal portion of the vertebral column, 

 being placed in advance of the ventrals. The adipose fin is always 

 present and well developed, although frequently short. The extent of 

 the anal is much inferior to that of the caudal vertebral column. The 

 gill membranes are not confluent with the skin of the isthmus, their 



