62 U.S. NATIONAL MUSEUM BULLETIN 282 



Type. — The types of Noiurus exilis Nelson have not been located. 

 They may have been destroyed in the Indiana University fire of 1883. 

 The type-locality is in McLean County, Illinois. 



Diagnosis. — Noturus exilis is the only member of the subgenus 

 Schilboedes typically having the combination: mouth terminal or 

 subterminal, jaws about equal, a single internasal pore, nine pelvic 

 rays, and ten preoperculomandibular pores. It has 17 to 22 anal 

 rays; 8 to 10, usually 9 pelvic rays; 8 to 10, frequently 8, but mostly 

 9 soft pectoral rays; and 44 to 57 caudal rays. The vertical fin borders 

 are often black or darkened, and the posterior edge of the pectoral 

 spine always has distinct serrae. 



The shortened caudal fin distinguishes Noturus exilis from A^. 

 insignis and A^. noclurnus and the ten preoperculomandibular pores 

 segregate it from other species of the subgenus except gyrinus, lach- 

 neri, noctumus, and gilberti. In contrast to gilberti, the vertical fins 

 have dark borders, some of the abdomen and lower head has pig- 

 ment, and the spines are longer. In contrast to gyrinus and lachneri, 

 there are more pelvic rays . 



Description. — Other counts and measurements are given in tables 

 17 to 26. Head decidedly depressed, rather elongate, especiaUy in 

 front of eyes, by elongation of the mesethmoid; lower jaw terminal 

 or subterminal; eye small, 2.5 to 3.5 times in snout; humeral process 

 obscure in some populations, usually shorter than the width of the 

 pectoral spine exclusive of serrae; dorsal spine stout; pectoral spine 

 short, straight, with five to eight, occasionally as many as ten serrae 

 which are long, prominent, and usually straight, but sometimes 

 bent outward or inward or fused at the base; anterior serrae never 

 present on spine, instead there may be retrorse hooks or progressive 

 offsetting of the edge (pi. 3, fig. 3) ; adipose fin long and low, closely 

 united to the anterior caudal rays, without a notch ; caudal fin slightly 

 rounded behind; posterior corners of the premaxillary tooth patch 

 rounded, truncate, or projecting slightly backward. 



The soft dorsal fin has five (in 1), six (189), or seven (4) rays. Of 

 187 individuals from over the range the caudal fin usually has 16 to 

 20 (mean 18.39) upper simple rays, 17 to 20 (mean 19.11) branched 

 rays of which 8 are in the upper lobe (mean 8.02) and 10 to 12 (mean 

 11.09) are in the lower lobe, and 11 to 15 (mean 13.16) lower simple 

 rays. 



In the skeletons and stained specimens examined: vertebrae an- 

 terior to the anal fin origin 12 (in 1), 13 (12), 14 (1), or 15 (1); ossified 

 pectoral radials fused (in 49 sides examined). The five or six hypurals, 

 at least in the specimens examined, are seldom fused; hypurals 1-3 

 were fused (in 1 specimen), 2-3 (in 3), and no fusion observed (in 

 13). There are five to eight gill rakers on the first arch. 



