214 U.S. NATIONAL MUSEUM BULLETIN 2 82 



overlap, are the result of the breakdown of isolating mechanisms 

 that exist between the two parents, especially where the population 

 size of one species is very small. It seems improbable that such hybrids, 

 although rare, result from accidental fertilization between species 

 that are solitary or nearly solitary in their nesting habits. 



Noturus exilis Nelson X Noturus miurus Jordan 



Plates 3 (fig. 11), 21 (fig. 1) 



Schilbeodes eleutherus (Jordan) [misidentifications]. — C. L. Hubbs, 1946, p. 

 38; and Hubbs and Lagler, 1947 [and 1949], p. 73 (Oklahoma, in part). — 

 Moore and Paden, 1950, p. 87 (Poteau R., Slate Ford, Okla. [erroneously 

 credited to Jordan and Gilbert]). — Bailey and Taylor, 1950, pp. 31, 38 

 (in part; Arkansas R. system).— Cross and Moore, 1952, p. 407 (Poteau R., 

 Slate Ford, Okla.) . 



Schilbeodes miurus (Jordan) X Schilbeodes nocturnus (Jordan and Gilbert) [mis- 

 identification]. — Taylor, in Cross and Moore, 1952, p. 407 (UMMZ 137904, 

 Poteau R., Slate Ford, Okla.). — Slastenenko, 1960, p. 75 (compiled). 



Material studied 



UNITED STATES: Oklahoma: UMMZ 137904 (1 specimen), Poteau R., 

 Slate Ford, near Shady Point, Le Flore Co., April 12, 1941. 



Description. — Reconsideration of this specimen, identified by 

 me as a hybrid between Schilbeodes miurus and Schilbeodes nocturnus 

 (see synonymy) , leads me to the firm belief that Noturus exilis rather 

 than Noturus nocturnus was one of the parents. There is no question 

 that Noturus miurus was the other parent. The single specimen is 

 from the Poteau River, a tributary of the Arkansas River in eastern 

 Oklahoma. It is compared with Noturus miurus, N. exilis, and N. 

 nocturnus in table 16. 



Body rather short, heaviest forward; caudal peduncle tapering 

 posteriorly; head broad, prominently depressed; lower jaw virtually 

 terminal; premaxUlary tooth patch with angulate posterior corners; 

 eye 2.3 times in snout; humeral process prominent, a little longer 

 than width of pectoral spine; pectoral spine (pi. 3, fig. 11) rather short, 

 curved backward; its anterior edge with irregidarities or roughenings 

 suggesting vestigial serrae; posterior serrae prominent and regularly 

 arranged but short in relation to diameter of spine; dorsal spine stout; 

 adipose fin moderately long and high, broadly united to the moderately 

 tall procurrent caudal fin; caudal fin tapers backward toward a point, 

 middle rays very long, with a rounded posterior margin. 



The individual is a male, 51.1 mm. in standard length. There are 

 5 + 10 = 15 anal rays, 24 + 7 + 10 + 15 = 56 caudal rays, 6 soft 

 dorsal rays, 36 vertebrae, 7 distinct posterior pectoral spine serrae 

 on the left side and 8 on the right. On each side there are nine pelvic 

 rays, nine soft pectoral rays, ten preoperculomandibular pores, a 

 single internasal pore, and six gill rakers. The least depth of the 



