1942 Bidletin //, United States National Mnseum. 



Cottopsis, GiEAED, Proc. Bost. Soc. Nat. Hist., iii, 1850, 303 (asper). 

 Potamocottus, Gill, Proc. Bost. Soc. Nat. Hist., vin, 1861, 40 (punctulatus). 

 jTaHridea, Jordan & Rice, Mau. Vert. E. U. S., Ed. 2, 255, 1878 (ricei). 



Fresh water scul])iu8. Body fusiform. Head feeldy armed ; skin smooth 

 or more or less velvety, its pricklrs, if present, not bony or scale-like; 

 \illiform teeth ou jaws and vomer, and sometimes on palatines. Gill 

 openings separated by a wide isthmus, over which the membranes do not 

 form a fold; no slit behind fourth gill. Branchiostegals 6. Dorsals nearly 

 or (luite separate, the tirst of 6 to 9 slender spines; ventrals moderate, 

 each with a short concealed spine and 4 soft rays. Lateral line present, 

 usually more or less chain-like, sometimes incomplete. Preopercle with a 

 simple spine at its angle which is usually curved upward, its base more 

 or less covered by skin, very rarely obsolete; usually 2 or 3 spines turned 

 downward below this; suboperele usually with a concave spine turned 

 downward. Yertebr;e 10 + 23^:33; pyloric cteca about 4. Fishes of small 

 size, inhabiting clear waters in the northern parts of Europe, Asia, and 

 America. The species are extremely numerous, and are very difficult to 

 distinguish, all being very similar in form, coloration, and habits. It is 

 probable that these are descended from some Asiatic marine type, as 

 TracJiidenmis {Centridermichtliys) rather than from MijoxocephaJus. In this 

 case Coitus asper would approach more nearly to the ancestral form. From 

 it are descended Coitus scmiscahcr and Coitua ictalops, with their multitude 

 of variations. Coitus (jobio, ahutieus, pliilonips, and poJJicaris indicate the 

 possible descent of Uranidca. In like manner Trif/lopsis seems to be de- 

 scended through Oncocottus from Myojocepkalus. The Miller' s Thumb, or 

 Blob, is found in most streams and lakes where trout occur, and it is one 

 of the most destructive enemies of the trout, devouring its eggs in great 

 numbers. (Coitus ; xdrzoc., an old name of the European Miller's Thumb, 

 Coitus (joJ)io, Linn;eus, from norra head.) 



a. Palatine bones each with a baud of teeth (these rarely few in number or wholly 

 absent). 

 Pegedictis {nriyTi, fountain; ix^v?, fish) : 



b. Preopercular spine short, hooked upward, partially or wholly concealed by 

 skin; 2 or 3 smaller spines directed downward below it. 

 c. Anal rays 15 to 20; back and sides smooth or variously prickly. 

 d. Body robust; head rounded anteriorly. 



e. Vent midway between base of caudal and tip of snout. 



ASPER, 2314. 

 ee. Vent nearer base of caudal than tip of snout. 



GULOSUS, 2315. 

 dd. Body long and slender; head narrowing rapidly forward, the snout 

 acutely rounded. evermanni, 2316. 



cc. Anal rays 11 to 15. 



/. Head narrowed anteriorly, the snout long; lateral line complete; 

 back and sides coarsely prickly, sometimes smooth. 



RHOTHEUS, 2317. 



//. Head more or less blunt and rounded in outline anteriorly; the 



snout short. 



g. Anal rays 13 to 15, usually 15; caudal peduncle stout; skin 



smootii. SHASTA, 2318. 



