GREAT LAKES COREGONIDS 



517 



profile of the head is straight. The cheeks are nearly flat, converging slightly in a 

 downward direction. The dorsal surface is triangular. The sides of the triangle 

 converge gradually from its base at the occiput, so that the snout is not sharply 

 compressed and its apex is rounded in front by the retrorse premaxillaries. The 

 width of the head through the nares is about 22 to 23 per cent of its length. A heavy 

 median keel, becoming heaviest in the center of its course, runs from the occiput to 

 the premaxillaries; as a result, the cranial surface is distinctly convex from side to 

 side. The ventral surface is like the dorsal, but nearly flat from side to side. The 

 branchiostegal membrane is supported by (8) 9-10 rays. Their proximal margins 

 run in a nearly smooth line with the outer lateral margin of the longest ray, so that 

 the entire figure is saber shaped. The borders of the isthmus are only slightly con- 

 vergent and join the mandible without uniting. The mandible is not conspicuously 

 compressed. The premaxillaries are wider (dorso-ventral measurement) than long 

 and are retrorse in position, making the mouth inferior. The extent of their back- 

 ward slant determines the shape of the snout, which may be elongate and tapering 

 or nearly truncate. Its length is contained in the head length (3.2) 3.4-3.7 (4.1) 

 times and is nearly equal to the short maxillary, which is contained (3) 3.2-3.4 (3.8) 

 times. The maxillary is always pigmented and seldom extends beyond the anterior 

 edge of the pupil. The eye is relatively small, decreasing conspicuously in relative 

 size with age, and is contained between 3.8 and 5 times in the head in the specimens 

 examined. For specimens under 250 millimeters in length the value is usually 3.9-4.3 ; 

 in specimens 250 to 350 millimeters long 4.4-4.8, and in larger fish more than 4.8. 

 The pupil is roundish, with usually a conspicuous angle in front, from which charac- 

 teristic the name Coregonus has been applied to such fishes. The gill rakers on the 

 first branchial arch are (9) 10-11 (12) + (14) 16-17 (19) = (24) 26-28 (30). 66 



The scales in the lateral line number (74) 81-88 (93). 67 Scale rows 68 around 

 the body just in front of the dorsal and ventrals number (46) 48-50 (52); in front 

 of the adipose and anus, (36) 37-39 (40); around the caudal peduncle at its com- 

 mencement, 25-27 (28). The length of the pectorals in contained (1.5) 1.7-2 (2.3) 

 times in the distance from their origin to that of the ventrals. The ventral length 

 is contained (1.3) 1.5-1.8 (2) times in the distance between their origin and that of 

 the anal. The adipose is scaled often to one-third its extent and is variable in size. 

 There are (10) 11 (12) 68 dorsal, ventral, and anal rays and (14) 15-16 (17) 68 pec- 

 toral rays. (See also fig. 12.) 



The color in life has been recorded incompletely but is not different from that 

 given under this heading for the Lake Superior form. 



COLOR IN ALCOHOL 



Most of the specimens preserved show the entire dorsal surface suffused with a 

 more or less smoky, sometimes nearly black, hue, which diminishes in intensity to 

 the lateral line and is absent below it, though pigment dots are present to the 

 belly. The hue on the back is often darkest in front of the nares, descending onto 

 the retrorse premaxillaries but usually stopping abruptly before reaching their 



68 One hundred and fifty-one specimens. 

 W One hundred and ninety-one specimens. 

 6 » Twenty specimens. 



