110 U.S. NATIONAL MUSEUM BULLETIN 282 



Rabida and other Schilbeodes, the band of teeth is a short block, 

 usually indented laterally; there is often a short extension posteriorly 

 of the bone on each side. Sometinies these extensions bear short teeth 

 that may be covered with flesh and visible only after the flesh is re- 

 moved. This is true of large specimens of Noturus exilis. 



After examining the species of the genus in which skeletons were 

 available, it was found that N. jlavus differs from the other species 

 chiefly in the extreme degree of development of the backward toothed 

 process. In adults, however, there is no overlap of this character 

 between flamis and other species of the genus. The width of the band 

 is about 1.5 to 2.5 times the least length. 



Noturus jlavus has two ossified pectoral radials on each side. In 

 other species of the genus these fuse or tend to fuse at an early age 

 but no tendency towards fusion has been noted in jlavus. The lower 

 jaw is included. The high number of caudal rays is interpreted as of no 

 particular significance. There are usually eleven preoperculomandib- 

 ular pores, the mode for the genus. The anal fin with 15 to 18, rarely 

 19 rays is of moderate length. The head is relatively large, and is 

 projected 3.3 to 3.8 times in the standard length. The skeleton is well 

 ossified, perhaps a factor associated with the greater size attained. 

 The vertebral number averages higher than in other species of the 

 genus, but is closely approximated by A^. exilis, N. gilberti, and N. 

 insignis. The origin of the anal fin is slightly farther back than in 

 other species, with the exception of A^. gilberti. In 14 specimens of 

 A'', jlavus there are typically 14 or 15 vertebrae anterior to the end 

 of the first pterygiophore of the anal fin. This high number is 

 duplicated in A^. gilberti and is approximated in N. insignis and N. 

 exilis. The high number of precaudal vertebrae (11 or 12) is also over- 

 lapped slightly by N. insignis and A^. juriosus; the number of caudal 

 vertebrae overlaps those of many members of the other subgenera. 

 Noturus jlavus, however, is the only species of the genus that usually 

 has nine ribs (range, 8 to 10); others typically have eight or fewer, 

 seldom nine. There are ten branchiostegal rays as in many other 

 Noturus. There is typically one epural. The six (3 + 3) or sometimes 

 seven (3+4) hypurals are seldom fused, at least in small to medium 

 size specimens. 



In Noturus jlavus, as in the subgenus Schilbeodes, the number of 

 branched caudal rays is relatively high (16 to 22, usually 17 to 20), 

 but the rays are only of moderate length. In species of Schilbeodes 

 other than N. gilberti and A^. leptacanthus the usual number is 17 or 

 greater; species of Rabida usually have fewer branched rays. 



A^. jlavus is relatively northern in distribution and extends farther 

 westward than any other species of Noturus. It prefers fast water in 

 large streams, and is commonly associated with a rocky bottom. 



