Figure 124. Sahelinus alpinus. Head from a male 

 about 600 mm long, from Kungmiut, western Green- 

 land. After Jensen. 



5 04 Memoir Sears Foundation for Marine Research 



caudal fin (at most a moderately concave one), a relatively broad bone in the ethmoid 

 position, a more or less rounded frontal region in the skull, not more than 50 gastric 

 caeca, and various skull characters as well as differences in the caudal skeleton, ^ ex- 

 cludes namaycush Walbaum (North American lake trout), for which Gill and Jordan 

 founded the genus Cristivomer. Vladykov has revived Baione DeKay as a subgenus of 



Sahelinus for the species fontinalis {6y : 

 928), which, according to him, is charac- 

 terized by a "little forked tail, black stripe 

 on lower fins, the absence of hyoid teeth, 

 and an uninterrupted row of vomerine 

 and palatine teeth." But Walters has 

 found that in some specimens of the com- 

 panion species alpinus the vomerine and 

 palatine teeth also form an uninterrupted 

 row (yo: 258, 260, fig. 14). Neither do 

 small differences in color seem to me to 

 provide a sufficient basis for subgeneric 

 separation in a genus where local popu- 

 lations vary as widely in this respect as 

 they do in Sahelinus \ nor does the pres- 

 ence or absence of hyoid teeth serve any practical purpose in this case, whatever the 

 phylogenic implication of differences in this respect. 



Species. The species remaining in Sahelinus after Cristivomer namaycush is excluded 

 fall in two divisions, the one typified by what may be termed the ''fontinalis complex," 

 the common brook trouts of North America (p. 525), the other by the "alpinus com- 

 plex," the Arctic-subarctic charrs (p. 507). Regan characterized these two divisions as 

 follows {^5: 408): 



S. alpinus division : head of the vomer with posterior process little developed. No 

 dark spots or markings. Circumpolar. 



S. fontinalis division: head of the vomer with posterior process well developed. 

 Blackish or dark olivaceous markings on back and on dorsal and caudal fins. North 

 America. 



The shape of the head of the vomer, however, is not a convenient aid for identi- 

 fication, for careful examination of the lower surface of the anterior part of the 

 skull is required. But the color pattern does afford a reliable field mark, not only for 

 freshwater populations of alpinus and fontinalis but even for those taken in brackish 

 or salt water; specimens of S. fontinalis always retain some trace of the wavy dark 

 markings on the dorsal and upper part of caudal, even though similar marks may dis- 

 appear entirely from the back and sides when the fish leave fresh water, or shortly 

 before. Further, the alpinus division, compared to xht fontinalis division, has the smaller 



2. For further details, including the history of the case, see Kendall (,/6: 78-81), and especially Vladykov 

 {67: 932). 



