828 



SCANDINAVIAN I-ISIIE.S. 



Sal,, 



Genus Osuierus. 

 Genus MallotH-^. 



Genus T/n/uicilliis. 



f;it for tilt' time when tliey must resort to fresh water 

 for tlie rejiroduetioii (A' tlieir species. 



Tiie Seiuidinaviaii .ireiiera of tliis family are the 

 followiii^U': 



A: Dentition strong, even tlie tongue fui- 

 nislied with teetli. Length of the maxil- 

 larics more than 53 %" of that of the head 

 reduced (from the hind extremity of the 

 intermaxillary bone to the posterior mar- 

 gin of the preoperculum). Base of the 

 dorsal fin proper shorter tlum the head 

 reduced. (Salmoinun') 

 1 : Branched rays in the anal finlessthanlT. 

 a: Transverse rows of scales on the 

 sides of the body more than 100. 

 /'.• Transverse rows of scales on th( 



sides of the body less than 80 



2: Branched ravs in the anal fin at least 17 

 B: Dentition weak or teeth w-anting, at least 

 the tongue toothless''. Length of the ma- 

 .xillaries less than 53 'o of that of the 

 head reduced. {Coregoniiur) 

 1: Base of the dorsal fin proper more 

 than 15 % of the length of the body 

 and longer than the head reduced . 

 2: Base of the dorsal fin proper less than 

 15 % of the length of the body. 

 a: Base of the dorsal fin ]iroper more 

 than half the length of the head 



reduced ■ -- Genus Coregonus. 



h: Base of the dorsal fin less than half 



(<45<) the length ofthe head reduced Genus Arqentina. 



In this manner we liaAe endeavoured to find an 

 expression for the said two directions of development. 

 The development, however, has not been so regular that 

 a sharp and fi.xed line can be drawn between two di- 

 stinct subfamilies; and the intermediate position occupied 

 by the Graylings (genus TlnjmaUus) may perhaps justify 

 the establishment of a third subfamily, characterized 

 principally by the advanced development of the dorsal 

 fin. The comnuinity of origin in the case of all these 

 genera affords an explanation of tlie fact that the fry 

 of the most differentiated forms in one group show 

 jioints of resemblance to tlie other group. 



In order rightly to comprehend the relations be- 

 tween the genera, it is indeed necessary to have a 

 knowledge of the exotic forms as well. But two of the 

 Scandinavian genera are so rich in forms, even within 

 the limits of our fauna, that in them we maj- trace the 

 development of form in its ])ast course and, seemingly, 

 in its present continuation. 



\ 



Fig. 208. A gravid female Smelt, taken at Stockholm on the 19th 

 of April, 1892. Natural size, ois, left ovary, with eggs arranged in 

 transverse rows; ovd, lower (posterior) part of the right ovary; m, 

 margin of the mesoariuin, which envelops the ovary both above (in 

 front) and below (behind) even on the left (outer) side, but below, 

 owing to the coalescence of the margin with the wall of the abdomi- 

 nal cavity, forms a funnel-shaped duct, open above at a; r, rectum; 

 an, vent; gu, situation of the genital and nrefliral apertures, the for- 

 mer in front of the latter, drawn as a common opening because the 

 wall between them could not be distinguished externally. 



" Exceptions occur amc^ng Sahnou fry. 

 ' ,1 ,) 11 Grayling ,, 



