326 FISHES OF ILLINOIS 



The sculpins chiefly inhabit rocky pools and shores of 

 northern regions; many species found in inland waters; genera 

 about 60; species 250. None are valued as food. 



Key to Genera and Species of COTTID^E found in Illinois 



a. Ventrals with a concealed spine and four soft rays Cottus. 



b. Preopercular spine short, usually inconspicuous, usually less than y 2 eye; 



interorbital space nearly as wide as or wider than eye, 3.8 to 5.6 in head; 

 depth of caudal peduncle 1.5 to 2 in its length; maxillary to middle of 

 eye; dark cross-bars usually present ictalops. 



bb. Preopercular spine long-, % to as long as* eye, strongly curved upward, back- 

 ward, and inward, the skin of the head carried upward by the spine on 

 each side in an ear-like manner; top of head flat, the interorbital space 

 very narrow, little more than half of eye and contained 8 times in head, 

 the eyes directed nearly upward; caudal peduncle very slender, its depth 

 about 3.3 in its length; maxillary scarcely past front of orbit; color 

 spotted or mottled, without distinct cross-bars ricei. 



aa. Ventrals with a concealed spine and three soft rays Uranidea. 



c. Preopercular spine less than % eye; interorbital space about half of eye, 7.5 



to 8.5 in head; caudal peduncle moderately slender, its depth 2.2 to 2.4 

 in its length; maxillary to middle of orbit; sides irregularly spotted, with- 

 out bars kumlienii. 



Genus COTTUS (Artedi) Linnaeus 



miller's thumbs 



Body fusiform, skin smooth or more or less velvety, prickles, if present, 

 not bony or scale-like; preopercle with a simple spine at its angle, which is 

 usually curved upward, its base more or less covered with skin, rarely obsolete; 

 gill-membranes separated by a wide isthmus, over which the membranes do 

 not form a fold; no slit behind fourth gill; villiform teeth on jaws and vomer, 

 and sometimes on palatines; dorsals nearly or quite separate; ventrals each 

 with a concealed spine and 4 soft rays; lateral line present. These are sculpins 

 of small size, inhabiting clear waters of the northern portions of Europe, Asia, 

 and America; species numerous. 



COTTUS ICTALOPS (Rafinesque) 

 common sculpin; miller's thumb 



(Pl. p. 300) 



Rafinesque, 1820, Ichth. Oh., 85 (Pegedictis). 



G., II, 158 (richardsoni); J. & G., 696 (richardsoni); M. V., 149 (richardsoni) ; J. 

 & E., II, 1950; N., 41 (Pegedichthys alvordi); J., 50 (Potamocottus alvordi, 

 wilsoni, and meridionalis) ; F. F., I. 6, 68 (Potamocottus meridionalis) ; F., 62 

 (Uranidea richardsoni); L., 30. 



Length 3 to 7 inches' body robust forward, subcylindrical, tapering 

 rapidly back of spinous dorsal; depth 3.7 to 4.3; width about z /i depth; depth 

 caudal peduncle 1.5 to 2 in its length. Color "olivaceous, more or less barred 



> * According to Jordan and Evermann; our single specimen with spine % of eye. 



