CATFISH GENUS NOTURUS RAFINESQUE 219 



Pylodictis and Satan has had nearly as long an ancestry, but that 

 line either has not speciated extensively or the relatives have become 

 extinct. Pylodictis, with a well serrated pectoral spine, modified 

 teeth, and a short adipose fin, and Satan, adapted to a cave habitat, 

 are undoubtedly highly modified from this old line. They may be 

 postulated to have arisen from a form not greatly unlike some species 

 of Noturus of the subgenus Rabida. In Pylodictis and Rabida similarity 

 exists in the presence of serrae on both edges of their pectoral spines; 

 both usually have nine or ten pelvic rays; both, at least as young, 

 have a variegated color pattern; in the Pylodictis group the sensory 

 canals of the lower jaw unite at the midline, or open from a median 

 pit, while in the subgenus Rabida the anterior pores often approach 

 the medial position and actually open from a common pit in some 

 individuals, and both have relatively high adipose fins and short anal 

 fins. 



Ictalurus is relatively less specialized than Noturus, but undoubt- 

 edly arose from a form like that postulated for an ancestral Noturus: 

 with eight pelvic rays, a continuous adipose fin, probably a relatively 

 small size, a weak and poorly armed pectoral spine, a short chunky 

 body, and a sHghtly arched skull. In Ictalurus, it is likely that the 

 bullheads appeared first; they are known as early fossils, have the 

 simplest structures, and are probably the most generalized ecologi- 

 cally. From this ancestral stock, the series of specializations grade in 

 the direction of Ictalurus punctaius on the one hand and Ictalurus 

 jurcatus on the other. In the first, evolution has left several variously 

 speciaUzed forms in Mexico and the southwestern United States and 

 Ictalurus caius along the eastern seaboard of the United States. The 

 probable furcatus group is represented in Mexico by an endemic 

 species of the Balsas basin, Ictalurus balsanus, in addition to the 

 wide ranging Ictalurus furcatus. The bullheads, which are generalized 

 and highly successful, have persisted in eastern North America. 



The apparent close relatives of each species of Noturus are indicated 

 in the discussion of the species. Those species of the subgenus Rabida 

 form a relatively compact group with considerable specialization in 

 development of spine serrae. In this subgenus the morphology grades 

 from elongate forms with eight pelvic rays and small, poorly armed 

 spines through those with nine rays to the relatively short, heavy 

 bodied forms with nine pelvic rays and large, well serrated spines. 

 Correlated with the increase in spine size is the increase in length of 

 the humeral process or posterior spine of the cleithrum and to some 

 extent the reduction of the adipose fin. Only the intermediate No- 

 turus eleuiherus and the relatively primitive Noturus hildebrandi lautus 

 have ten preoperculomandibular pores. The lower jaw is included in 

 all species, but it approaches the interpreted generalized condition 

 in Noturus baileyi. 



298-943 O — 69 15 



