298 LAKE SUPERIOR. 



differ in very different amounts of variation, and nevertheless con- 

 stitute, at least in the eye of the deeper investigator, a very natural 

 group ; such, for instance, is the family of Cottoids, such again is 

 the family of Scomberoids. The difficulty in such cases is not the 

 diversity, but a correct appreciation of the connecting character, 

 which, if misunderstood, might bring together animals widely dis- 

 tinct in structure, but apparently related by external appearance ; for 

 instance, the genus Capros among Scomberoids, near Zeus, owing to 

 its form and the dilatability of the mouth, when in truth it belongs 

 to the Chsetodonts, in the vicinity of Chelmo. 



Taking for granted that the family of Cottoids, as it is now charac- 

 terized, is in the main a natural one, the question arises at once, 

 what can be done to appreciate correctly the true relations of those 

 remarkable tropical forms, as Pterois, Lynanceia, &c., with the 

 more uniform Cottus, Etheostoma, Gasterosteus, of the freshwaters 

 of temperate regions ? To become satisfied that they are truly 

 members of the same family, it is necessary to undertake an extensive 

 comparison of the structure of their head, and especially of the ar- 

 rangement of their infraorbital bones, when it is seen that frequently 

 the particular development which characterizes, generally, this 

 group, is reduced to a rudimentary state in some of its members, as 

 in Etheostoma and the genera allied to it. This group of small 

 Cottoids having attracted less attention than the larger marine types, 

 we subjoin a synopsis of their genera. 



Subfamily of Etheostomata. 



Freshwater fishes of medium and small size, somewhat related to 

 the Gobii. Cheeks sometimes covered with scales, sometimes bare. 

 One small suborbital bone only, the anterior. Mouth variable. 

 Head sometimes elongated, sometimes truncated or rounded. Scales 

 proportionally large. No air bladder. No pseudo-branchiae. Teeth 

 very minute. 



Etheostoma, Rafin. 

 .Head elongated, pointed ; mouth widely open, not protractile, 



