FISHES — SALMONIDAE — COREGONUS WILLIAMSONI. 



327 



the extremity of the snout. Scales well developed, disposed upon eighteen longitudinal series across the line of tlie greatest 

 depth : nine between the lateral line and the base of the dorsal, and eight between the lateral line and the insertion of the 

 ventrals. Bluish lead above ; whitish beneath, with a silvery reflect. 



Stn. — Coregonm icilliamsoni, Grd. in Proc. Acad. Nat. Sc. Philad. VIII, 1856, 136. 



Two specimens of the female sex have been preserved, the total length of either measuring 

 ahout eleven inches. The body is elongated, rather stout, sub-fusiform in profile; the peduncle 

 of the tail well developed. The head is rather small, sub-conical or sub-pyramidal, terminated 

 by a truncated snout which protrudes beyond the lower jaw. The mouth is quite small ; the 

 maxillar bone being proportionally very broad, but so short that its posterior margin scarcely 

 reaches, if at all, a vertical line drawn in front of the orbit. The origin of the dorsal fin is 

 nearer the posterior margin of the base of the adipose than the extremity of the snout ; its 

 upper edge is sub-concave instead of being linear, as exhibited on the accompanying figure. 

 The anterior portion of the same fin is higher than its base is long. The adipose is well 

 developed, situated immediately opposite the anal fin. The latter is anteriorly deeper than 

 long ; its initial ray being nearly equidistant between the origin of the ventral fins and the 

 insertion of the caudal. The external margin of the anal fin is sub-convex also ; its own base 

 entering about eleven times in the total length ; twice in the length of the side of the head. 

 The ventrals are inserted opposite the posterior fourth of the base of the dorsal fin ; their 

 posterior margin is sub-truncated or rounded off, and when bent backwards their extremities 

 are very far from approximating the vent. The pectorals are sub-lanceolated, and, like the 

 ventrals, proportionally well developed. The caudal is furcated^ shorter than the head, since 

 it enters somewhat over six times in the total length. 



Br. VII : VII ; D 2, 12 -f 1 ; A 2, 12 + 1 ; C 5, 1, 9, 8, 1, 6 ; V 12 ; P 16. 



The scales are large, deeper than long, with their anterior margin undulating, rounded 

 sideways and posteriorly, slightly diminishing in depth. The four sections of the scales are 

 limited by a furrow ; the concentric lines are almost entirely obliterated upon the posterior 

 section ; no radiating furrows being observed on any of the sections. Eighteen longitudinal 

 rows of scales may be counted between the anterior margin of the dorsal and the insertion of 

 the ventrals : nine above the lateral line and eight below it. The lateral line itself is perfectly 

 straight. Large mucous ducts may be seen on the cheeks extending from the supratympanic 

 region to the snout. 



The upper region is bluish grey or lead, whilst the sides and belly are whitish, with a silvery 

 reflect all over. 



Beferences to the figures. — Plate LXXVI, lower figure, represents Coregoniis luilliamsoni, 

 somewhat reduced in size. Fig. at the upper left corner, a scale from the dorsal region. 

 Middle figure, a scale from the lateral line. Fig. at the upper right corner, a scale from 

 the abdominal region. 



List of specimens. 



