CATFISH GENUS NOTURUS RAFESTESQUE 109 



Pimelodus Lac^pede. The genus Noturus has either been treated as 

 monotypic or enlarged to include all the recognized species of Noturus. 



The unfused pectoral radials, the specialization of the premaxillary 

 tooth band, the greater numbers of pelvic and soft pectoral rays, 

 an increase in the numbers of certain skeletal parts, and the relatively 

 larger size attained are the chief characteristics of the subgenus. 

 These characters, in view of the great variation of the same characters 

 in other species of Noturus, are not worthy of use in the placement of 

 Noturus Jlavus in a monotypic genus. Since flavus may be closely 

 related to certain SchUbeodes, the discussion of characters is chiefly 

 in relation to the members of that subgenus. 



The moderately long, nearly straight, mostly unserrated pectoral 

 spine (pi. 3, fig. 10) shows no important differences from SchUbeodes; 

 indeed, the species of that subgenus have a wide range of variation in 

 shape and serrations that would virtually include all structures found 

 in Jlavus. There are no anterior serrae; the posterior serrae are irregu- 

 larly developed, usually indistinct and never uniformly turned toward 

 the spine base. The recurved anterior hooks or steps of the spine can 

 almost be duplicated in many individuals of A^. insignis; the short 

 grooves are moderate in depth and mostly distal on the spine. The 

 body is moderately elongate as is also true in several SchUbeodes. 

 The numbers of soft pectoral (9 to 11, modally 10) and pelvic (8 to 10, 

 modally 9) rays are higher in flavus than in any other group; however, 

 the high mean number of pelvic rays oi flavus is approached by N. 

 gUberti. These two species are the only forms without pigment on the 

 lower surface of the head and abdomen, and are superficially alike, 

 after preservation, in having broad light (immaculate) margins of the 

 vertical fins; otherwise ^azrus is yellowish, slate-gray, or olive green 

 above; it resembles exUis in having a yellowish spot beneath the 

 posterior end of the dorsal fin base; there are no prominent dark 

 blotches as in Rabida. 



The shape of the premaxillary tooth band appears to be of some 

 importance. The posterior extensions constitute undoubted special- 

 izations, but the function is not yet known. Posterior extensions of a 

 similar nature but of dissimilar shape and structure have appeared at 

 least twice in other genera of the family. Undoubtedly all three were 

 derived independently. In N. flavus (pi. 2, fig. 3) the extension is long 

 and narrow and emerges from the lateral corner of the otherwise 

 rectangular band; in Pylodictis olivaris (Rafinesque) the extension is 

 broad and long and emerges from the posterior edge; in Ictalurus 

 balsanus (Jordan and Snyder) the extension is from the posterior edge, 

 but is short and broad. In the genus Noturus, there is considerable 

 specific variation in the shape of the premaxillary tooth band. In 

 N. gyrinus, the transverse extent is greater than in other species; in 



