172 U.S. NATIONAL MUSEUM BULLETIN 2 82 



maculate; upper limb extends onto upper procurrent rays and down- 

 ward, indistinctly, into base of caudal peduncle; adipose fin mostly 

 immaculate, its broad, dusky blotch extending into only the basal one- 

 half of fin; below, the blotch grades into the mottled side; a dark or 

 dusky blotch is between the dorsal and adipose fins; the first dark 

 saddle extends from the dorsal fin to below the lateral line, backward 

 to the second dorsal ray, and forward as a narrow blotch along the 

 midline to a point midway between the dorsal spine and head; it may 

 enclose two small, faintly developed, predorsal light spots; membrane 

 over air bladder grayish. 



Type.— The holotype (UMMZ 167653) is a male, 43.0 mm. in 

 standard length. It has 4-|-10=14 anal rays, 20+8+9 + 17 = 54 

 caudal rays, and 6 soft dorsal rays. On both sides there are : nine pelvic 

 rays, eight soft pectoral rays, six serrae from posterior edge of pectoral 

 spine, two internasal pores, and eleven preoperculomandibular pores. 

 The head length is stepped into the standard length 3.35 times and the 

 distance from the end of the adipose fin to the tip of the caudal fin is 

 stepped into the distance from the origin of the dorsal fin to the end of 

 the adipose fin 1.55 times. Other measurements are given in table 28, 



Range. — Map 13 shows the distribution of this species. It occurs 

 in the Cottonwood River, throughout the Neosho River below 

 Emporia, Kansas, and in the lower few miles of the Illinois River, 

 Oklahoma. Cross (1967, p. 223) recorded specimens from the Spring 

 River, Kansas, a tributary of the Neosho River. 



Variation. — Other than the specimen mth 13 anal rays, counts 

 obtained from the Neosho River population overlap broadly those 

 from 5 Illinois River specimens. Probably there are no significant 

 differences in the structures studied between Illinois and Neosho 

 River specimens, and none is evident in pigmentation. Illinois River 

 fish are heavier bodied. 



Etymology. — The name placidus (Latin) means mild, quiet, or 

 gentle. It is used in allusion to the relatively poorly armed pectoral 

 spine in contrast with other members of this species group. 



Relationship. — Although the adipose blotch is poorly developed 

 and extends only into the basal portion of the fin, and the humeral 

 process is hardly longer than in Noturus eleutherus, the number of 

 preoperculomandibular pores, the pigmentation, especially the 

 tendency to form predorsal light spots in the saddle about the dorsal 

 fin, and the midcaudal crescentic bar, align this species with the 

 furiosus species group. 



Ecological considerations. — Noturus placidus has been taken 

 in collections containing A'", nocturnus, N. exilis, and N. flavus. In 

 the Illinois River, Oklahoma, it was taken close to a locality whence 

 A^. miurus was obtained. 



