66 FISHES OF PENNSYLVANIA. 
structure of the gill rakers and the size of the mouth. The remaining two white 
fishes have the lower jaw as long as, or ionger than, the upper ; the mouth large, and 
the intermaxillary narrow and not vertical in position. They are easily separated 
from each other by the shape of the body, and the size and contour of the scaies. 
The relations of the species are shown in the following key : 
1. Lower jaw shorter than upper. ss 
la. Mouth very small, upper jaw not reaching to eye; gill rakers short and 
stout, 13 to 16 below angle of first arch (Prosopium). 
QUADRILATERALIS. 
1b. Mouth moderate, upper jaw reaching beyona front of eye; gill rakers 
long and slender, 20 or more below angle of first arch (Coregonus). 
CLUPEIFORMIS. 
2. Lower jaw equal to or longer than upper. 
2a. Body sleuder, elongate ; scales small and convex on their free margin; 
lower jaw longer than upper (Argyrosomus). 
ARTEDI. 
2b. Body deep, short; scales large, deep, the free margin scarcely convex; 
jaws equal (Allosomus). 
TULLIBEE. 
84. Coregonus quadrilateralis Ricuarpson. 
The Round Whitefish. (Figure 47.) 
This is asmall species and very readily distinguished from all otner American 
species except Williamson’s whitefish by its diminutive mouth. The body is slen- 
der, elongate and subterete, its greatest depth slightly exceeding one-fifth of total 
length to base of caudal. The head is long, its length one-fifth of total without cau- 
dal, and the snout is thin and obtuse at tip. The broad maxilla does not reach to 
below the front of the eye; its length less than one-fifth length of head. D. 11; A. 
10 ; scales in lateral line, 80 to 90. Upper parts dark bluish; sides silvery. 
Names.—This species is called frost fish in the Adirondacks; other 
names are Menomonee whitefish, round-fish, shad-waiter, pilot-fish and 
chivey. ‘The last term is applied to the fish in Maine. 
Distribution.—The round-fish is found in lakes of New England, some- 
times running into streams, the Adirondack region of New York, the 
Great Lakes and northward into British America and Alaska. Its dis- 
tribution has been extended by transplanting on account of its great 
value as food for the lake trout and other large fish of the salmon family. 
Size.—It seldom exceeds a length of twelve inches and a weight of 
one pound. 
Habits.—Like some other species of whitefish it spawns in shallow 
parts of lakes or ascends their small tributary streams for that purpose, 
The food consists of small shells and crustaceans. The species fre- 
quents deep waters, where it falls an easy prey to the voracious lake trout. 
Uses and Capture.—The round-fish is excellent for the table, and as 
food for the larger trout and salmon it is unsurpassed. Its capture 
with hook and line is difficult, because of its very small mouth and its 
habit of retiring into deep water. In the Great Lakes it does not con- 
stitute an important element of the fishery, but in northern regions it is 
one of the most useful and highly prized of the food fishes. 
