36 BIOLOGICAL SOCIETY OF WASHINGTON. 



acteristic of its fish types are various forms of Nototheniidae, Perco- 

 phididte, Chilodactylines, Haplodactylines, and Agriopodidae. 

 The Selachian genus Callorhynchus is also limited to the realm. It 

 thus differs much from the Pararctalian, but, nevertheless, a num- 

 ber of genera, as was long ago shown, reappear in it, although 

 they are absent in the superficial waters of the tropics. 



V. THE ANTARCTALIAN REALM. 



Antarctalia, or the Antarctic realm, corresponds to Arctalia, 

 and may cover the antipodal ocean up the isocryme of 44°, (the only 

 continental area thus embraced being Patagonia) northwards on 

 the east to somewhere near or about the mouth of the Rio Negro, 

 and on the Pacific coast to about the latitude of 50° S. As a rule, 

 the fauna is very different from the Arctalian, and to some extent 

 the characteristic arctic types of fishes are represented by analogous 

 types of entirely diff"erent families, the role of the Gadidee being as- 

 sumed by Nototheniidge, and that of the Cottidce by Harpagiferidae 

 and Chcenichthyidae. Nevertheless, the Gadidae have an incon- 

 spicuous representative and the genera i^/)'x///^, Squahis {Acanthias), 

 and Merhuius have typical species scarcely or not at all differenti- 

 ated from their arctic allies. 



Lest an exaggerated idea should still be entertained as to the 

 demarcations of the several regions, I think it necessary to repeat 

 specially that not only are the exact limits of such not fixed or fix- 

 able, and variable even according to the season, but they may ac- 

 tually coexist in the same vertical, and one may be superposed 

 over the other, or the reverse. An example among many is to 

 be found off the New England coast. It has been repeatedly ad- 

 verted to by Prof. Verrill,^ and is familiar to many of you present. 

 Indeed, as I shall presently show, there are at varying depths hori- 

 zontal faunal assemblages of animals as well as those superficial or 

 shallow-water ones more familiar to most persons. 



*A. E. Verriix, in the Report of the U. S. Commission of Fish and Fisheries, 

 part I, pp. 484, 485. 1873. etc. 



