132 U.S. NATIONAL MUSEUM BULLETIN 2 82 



(humeral process) is associated with Noturus baileyi in the hildebrandi 

 species group. Both are readily distinguished from other species of the 

 subgenus Rabida by the presence of only eight pelvic rays. In contrast 

 to Noturus baileyi, there are typically eight or nine, more often nine, 

 instead of seven or eight soft pectoral rays, more anal rays (usually 

 13 to 15), and the lower jaw is definitely included instead of being 

 almost subterminal. The internasal pores are typically two on each 

 side but the preoperculomandibular pores, normally ten or eleven, 

 vary geographically. 



Description. — Counts and measurements are given in tables 

 17 to 26. Head depressed; lower jaw prominently included; lip rather 

 thick; eye moderate, about 1.4 to 2.5 times in snout; posterior process 

 of cleithrum very short or obscure, blunt to sharp pointed; pectoral 

 spine small, relatively straight (pi. 4, figs. 1, 2); its anterior serrae 

 small or obscure; its posterior serrae, except the proximal one or two, 

 recurved toward the spine base; dorsal spine small and stiff; adipose 

 fin of moderate height and length, without a free posterior flap, 

 broadly connected with the rather short procurrent caudal rays; 

 caudal fin truncate or with a slightly rounded posterior margin; 

 posterior corners of premaxillary tooth patch obtuse. The largest 

 specimen examined is one typical of the southern subspecies, from the 

 Homochitto River, 53 mm. in standard length. Typical specimens of 

 the northern subspecies reach 48 mm. in standard length. 



The soft dorsal rays are five (in 4), six (156), or seven (2). The 

 caudal fin has (extremes in parentheses) : (14) 16 to 18 (20) upper 

 simple rays; (13) 15 or 16 (17) branched rays of which (5) 7 (9) are in 

 the upper half of the fin and (6) 8 or 9 (10) are in the lower half; and 

 (11) 13 to 15 (17) lower simple rays. There are four to eight gill rakers 

 on the first arch. 



In six cleared and stained specimens, 12 (in 5) or 13 (1) vertebrae 

 are anterior to the origin of the anal fin; the ossified pectoral radials 

 are fused ; and the six hypurals show variable fusion distally ; hypurals 

 2-3 were fused in four specimens from the Homochitto drainage; 

 hypurals 2-3 and 4-5 were fused in two from western Tennessee. The 

 number of caudal vertebrae may also vary as follows: Homochitto 

 drainage 25 (2), 26 (1), or 27 (1); western Tennessee 28 (2). 



Relationship. — The characters listed in the diagnosis are regarded 

 as indicating, at least tentatively, the relationship of Noturus hilde- 

 brandi and Noturus baileyi in the hildebrandi species group. 



Discussion. — A study of the geographic distribution and char- 

 acteristics of populations of Noturus hildebrandi has revealed a 

 situation that appears to be unique among North American fishes. 

 No other eastern North American fish is known that has its range 



