SA LM0NID2E. 
891 
Genus COREGONUS. 
All the teeth of the mouth , except those on the tongue , as a rule soon disappearing during growth , or soon con- 
cealed in the gums , or persistent as scattered , fine , villiform, mobile teeth, or entirely wanting. Length of the 
maxillaries 50 ( exceptionally 52) — 32 %, and of the lower jaw 70 ( exceptionally 74) — 40 %, of that of the head 
reduced. Breadth of the snout across the articular knobs of the maxillaries perceptibly less than that of the in- 
terorbital space , which i is at least 1 / ' 4 (exceptionally 24 %) of the length of the head. Base of the dorsal fin less 
than 15 % of the length of the body, but more than half the length of the head reduced. Pyloric appendages 
well- dev el oped. Scales middle-sized, about 80 — 90 (exceptionally about 70- — 110) in the lateral line, 
which is complete. 
The dental reduction which we have seen in the 
preceding genera — in the strength of the teeth in 
Mallotus, and both in their strength and number in 
Thymallus — has advanced still further in the Gwyniad 
genus ( Cor eg onus ) towards the Cyprinoid type. The 
direction of the reduction is indeed not the same as 
in Thymallus, the teeth on the tongue being persistent, 
and sometimes even more developed than in Mallotus. 
But else the reduction is a continuation of that which 
we have seen in Thymallus, and in their form, the 
jaw-teeth, where they are present, come nearest to 
those of the Graylings. The maxillaries and the vomer 
are always toothless in Coregonus ; but on the inner 
(hind) surface of the intermaxillaries and on the an- 
terior part of the palatines the Gwyniads proper are 
usually furnished with teeth, on the former bones set in 
a thin transverse row and mobile as in Mugil, on the 
latter firm and pointed, but small. Among the true 
Gwyniads w r e find only dermal papilla instead of teeth 
in the lower jaw; but among the Vendaces small teeth 
sometimes occur in the anterior part of the lower jaw, 
as well as on the intermaxillaries®. In the pharynx, 
however, we find teeth, numerous though small, not 
only on the so-called pharyngeals, but also on the 
upper parts of the posterior branchial arches 6 . 
The reduction of the teeth is partly compensated, 
as usual, by the apparatus composed of the gill-rakers 
(fig. 222), which are subject in Coregonus to great 
variations, probably connected with variations in the 
diet of these fishes. The rule is apparently that, where 
the diet consists of large objects, principally fish, the 
Fig. 
A, 
B , 
C, 
D, 
E, 
F, 
gill-rakers (45) and branchial lamellae on the first left 
branchial arch in a Vendace ( Core- 
gonus albula). 
,, (60) on the first left branchial arch in a 
Felet ( Coregonus cyprinoides). 
,, (45) on the first left branchial arch in an 
Asp-Gwyniad ( Coregonus aspius). 
,, (27)1 on the first left branchial arch in a 
,, (25)1 Gwyniad ( Coregonus lavaretus). 
,, (20) on the first left branchial arch in a 
Polcur ( Coregonus polcur). 
Figs. B — F after Widegren. 
Smitt, 1. c., tab. metr. VIII, Uoregoni, note to specimen No. 5. 
See above, p. 523, note a. 
