CATFISH GENUS NOTURUS RATESrESQUE 129 



radials usually fused, but some species, chiefly Noturus stigmosus, 

 vary in the amount of union of the two elements; all species typically 

 have one epural and 3 + 3 hypurals, with variable fusion in each set 

 of hypurals. The skeleton is not well ossified, perhaps because of the 

 small size attained. The premaxillary teeth (pi. 2, fig. 4) occupy a short 

 rectangular area which is about 1.5 to 2.5 times as broad as long, 

 with rounded to obtusely angulate posterior corners. All the species 

 are mottled or covered \\dth irregular dark blotches or saddles. In 

 young or small specimens the adipose fin is distinctively translucent 

 or clear. The background color of the body may be pinkish, yellowish, 

 or brownish, becoming darker mth age. 



The included species have been uniformly listed as a unit in either 

 the genus Noturus, or Rahida, or SchUheodes; they have never been 

 spHt into separate genera. However, when Rabida has been recognized, 

 authors have tended to include in it one or more of the species in the 

 subgenus SchUheodes that have posterior serrations on the spine. 

 SchUheodes has thus been split unnaturally into two or more groups. 



With the exception of one that is found in Atlantic coastal streams 

 of North Carolina, the species are restricted to tributaries of the 

 Gulf of Mexico or have invaded the lower Great Lakes after recession 

 of the Wisconsin ice. Most species, except Noturus miurus, seem to 

 require a considerable stream gradient and are found at or near 

 rifiles. 



Noturus furlosus, the North Carolina representative, appears to 

 be a segment of a once wide-ranging species which may have occurred 

 in most preglacial rivers of eastern North America. A^. stigmosus and 

 N. miurus have crossed into the Great Lakes basin, probably by way 

 of the Maumee outlet. N. munitu^ and N. miurus are perhaps recent 

 invaders of Gulf tributaries lying to the east of the Mississippi River. 

 Invasion of this area by N. miurus probably was a simple matter, 

 because of its tendency to enter small and quiet waters. However, 

 invasion by N. munitus (a river species) probably called for large 

 quantities of flowing, fresh water such as a major shift in river drain- 

 age, overflow by an overburdened Mississippi River, or by a fresh- 

 water concentration in what is now the Gulf of Mexico adjacent to 

 the mouths of the Mississippi and Mobile Rivers. Another possibility 

 is that munitus has remained as a remnant of the former more widely 

 distributed ancestor of the furiosu^ group. 



With these exceptions the species are confined to the Ohio, the 

 Tennessee, the lower Mississippi, and the Red River drainages. 

 A^. miurus has crossed over into the upper Kaskaskia River, Illinois; 

 otherwise no member of the subgenus has entered the upper Missis- 

 sippi or the Missouri River systems. The forms are especially char- 



