CATFISH GENUS NOTURUS RAFINESQUE 217 



separation of the North American species as a family will hold. Study 

 of the ictalurids indicates a lack of diverse modification in most organ 

 systems and suggests a monophyletic origin. The principal differences 

 in groups and species result from loss or accentuation of parts. 



A comparison of the genera of the family Ictaluridae is presented 

 in table 1. The genera seem to fall into three major divisions: the 

 Pylodictis group containing that genus and Satan; the Noturus group, 

 encompassing also Prietella; and the Ictalurus group, including 

 Ictalurus and Trogloglanis . That the genera in each group are related 

 is evidenced by their structural similarity. Adaptation to under- 

 ground life, eyelessness, depigmentation, and absence of the air bladder 

 are regarded as extreme specializations in Satan and Trogloglanis. In 

 the latter, the backward extension of the supraoccipital process is 

 extreme and is equaled only in a few highly modified species of 

 Ictalurus; the loss of teeth on the jaws is unique in the family. Noturus 

 and Prietella are similar in many characters but dissimilar in others 

 suggesting early divergence from a common ancestor. Prietella has 

 apparently adopted a subterranean life, with loss of eyes and pig- 

 ment, and reduction of the skeleton. Yet in the retention of a poorly 

 ossified, mostly segmented, first long dorsal ray it is much more 

 primitive than Noturus. As judged from the sensory canal system 

 and the number of pelvic rays, the Noturus group is intermediate 

 between the Ictalurus and Pylodictis groups. In certain features it is 

 unlike them, and has undergone specialization from the presumed 

 ancestral stock, for example in the extreme reduction or loss of the 

 post-temporal bone and in the reduction of elements in the skull and 

 pectoral girdle. Noturus and the blind species still retain a "primitive 

 finfold," exemplified in the connected adipose and caudal fins, and 

 their skeletons are typically weak and not heavily ossified. 



The presence of eight pelvic rays in Prietella and eight or nine in the 

 forms of Noturus may indicate a transition from eight in Ictalurus to 

 nine or ten in the Pylodictis group. Such an evolutionary increase is 

 suggested since many bagrids and pimelodids have six pelvic rays, and 

 in the the Ictaluridae there is a tendency for specimens to have in 

 excess of the modal number of pelvic rays more frequently than fewer 

 (general observation and table 18). In an 8-rayed species, a count of 

 seven rays is rare, whereas nine rays is occasional ; in 9-rayed species, 

 ten pelvic rays are encountered much more frequently than eight. 



The direction of change in the spines undoubtedly was consolidation 

 and development of spinules or serrae. At one extreme is the strongly 

 serrated, large, specialized pectoral spine such as that of Noturus 

 juriosus and at the other a straight, simple, and poorly consolidated 

 structure such as in Noturus gyrinus. This trend is repeated in the 

 complex structure of the spine of Ictalurus 'punctatus contrasted to the 

 simpler spine of Ictalurus mela^. 



