96 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 
way the Isospoiidylous fishes are nearest the Ilalecomorphi, and have 
probably descended from some Crossopterygian, near the Maplistia, 
through that order. The affinity of the cat-fishes to the sturgeons is 
seen in the absence of symi^lectic, the rudimental maxillary bone, and, 
as observed by Parker, inHhe interclavicles. There is a superficial 
resemblance in the dermal bones.” {Cope. 1. c., 454.) 
This groui) comprises the Siluridce and their relatives, now divided 
into several families by Professor Gill, {vrjp-a, thread j 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. ..Siluridje, 29. 
Family XXIX.— SILURIDJE. 
{The Cat-fislm.) 
Body more or less elongate, naked or covered with bony j)lates. 
No true scales. Anterior part of head with 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 tie organ of hearing by means of the auditory ossi- 
cles. Lower pharyngeals seiiarate. 
After the removal of numerous aberrant forms as distinct families, 
the family of SiluridcCj 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 mostly tropical. 
Our species all belong to the division called by Dr. Gunther, Siluridce 
Proteropterce, and thus characterized : 
“ The raj' ed 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 
