CO'lTOIUS. 



169 



Dkkav", luiwevcr, Ii.mI previously a(lo|)tt'cl one of the 

 AiiK'i'i(/ini tVcsli-wiitci' CoUi MS the 1v|(c of ;i new geiiiis, 

 l'nii/i(Je(i, a name whidi lias thus uu older claiui to 

 eu^plo^"UleMt, e\'en thouiiii this claim was duiiious, so 

 long as only one species of the geuus was known. 

 In a grou]) so naturally connected as that of the ('off/, 

 it is always con\ enience, the con\'enieuce nee(U'(l to 

 facilitate tlie inspection of a genus, tliat in the first 

 ])lace decides the necessity of its systematic division; 

 and in a local i'anna, where the inuuher of species is 

 no greater tlian, for example, in Scandinavia, this 

 question loses a great part of its importance. Lutken 

 has pointed out'' the impossibility of maintaining the 

 distinctions between these genera l)y the helj) of fixed 

 characters. Fixed characters are ho\\ever to l)e found. 

 The fact that a fish lives in fresh ^vater is in itself l)y 

 no means a sufficient ground for its systematic isolation 

 — the River Bullhead occurs in the Baltic, and the 

 Kour-horned Cottus lives in the larger Swedish lakes — 

 but this manner of life, probably, has set on the fresh- 

 water Cotti an impress of the juvenile stages in the 

 development of the others, which also attain a greater 

 size than they. One apparent ])roof of this is the fact 

 that in Lake Wetter youTig specimens of the Four- 

 horned Cottus have a smaller head than those of the 

 same age in the Baltic or the Arctic Ocean. Again, 

 the River Bullhead and its relative the Alpine Bull- 

 head {Cottus poerilopiis) have the smallest head of all 

 the Scandinavian Cotti, and might be distinguished from 

 the others ])_y means of this character, liad not the 

 circumstance mentioned al)Ove caused an encroachment 

 of the character of the Four-horned Cottus in this re- 

 spect upon the limits of the variations of the Alpine 

 Bullhead. The above-mentioned characters given by 

 GiRARD to the fresh-water Cotti also hinge upon the 

 fact that they correspond to the juvenile stages of the 

 other Cotti. But the smaller size of the gape, com- 

 bined with another peculiarity, tlie length of the base 

 of the second dorsal fin, ^\•hich according' to our ob- 



servations is generally longer, form a constant character, 

 on w liicli we base our present adoption of the fresh- 

 water Cdltl as a distinct sul)genus. The species which 

 occur in the Scandinavian Fauna may Ije distinguished 

 l)y the help of the following table; 



A: Length of the maxiihny bones less tliaii 

 36 % aad the length of the lower jaw 

 less than 44 °<, of tlie length of the 

 base of the secoufl dorsal flu. Head 

 without spines on the top or on the 

 snout: — Subgenus Uranidea. 

 a: Length of the base of the anal fin 

 less than 48 % of the distanee be- 

 tween this fin and tlie tip of the 



snout Cottus goliio. 



h: Lcngtli of the base of the anal fin 

 more than .53 "« of the distance be- 

 tween this fin and the tip of the 



snout Cottus jioecilopus. 



B: Length of the maxillary bones more 

 than 38 % and the length of the lower 

 jaw more than .50 % of the length of 

 the base of the second dorsal fin. Head 

 with spines on the top as well as on 

 the snout: — ^wh^exiws Acantliocottus. 

 1 : Least dej^th of the tail less than 4*. ., 

 % of the length of the body and less 



than i\ K of the base of the anal fin Cottus cjuadricornis. 

 2: Least depth of the tail more than 

 4',.; -0 of the length of the body and 

 more than 24 % of the base of the 

 second dorsal fin. 



a: Lateralline smooth, with a down- 

 ward curve at the end of the 

 Second dorsal fin. Margins of 

 the branchiostegal membranes 

 united to each other by a free 

 dermal riap under the isthmus. 

 No dermal papilhv on the upper 



jaw-bone Cottus scorpius. 



b: Lateral line spinous, without any 

 visible curve in the posterior part. 

 Branchiostegal membranes united 

 to and separated by the isthmus. 

 At least one dermal papilla on 

 the posterior part of the upper 

 jaw-bone: 



«: Four ravs in the ventral fins Cottus huhalis. 

 (j: Three „ „ „ „ „ Cottus LiUjehorriii. 



" N. York Fn., vol. IV, Fi.^h , p. Gl. 



'' Vid. l\reddd. Naturh. For. Kbhvn, 187(5, p. 3(;6. 



Scandinavian Fishes. 



