MICROPTERUS — BLACK BASS 267 



MICROPTERUS SALMOIDES (Lacepede) 



LARGE-MOUTHED BLACK BASS 

 (Frontispiece; Map LXXXI) 



LacSpdde, 1802, Hist. Nat. Poiss., 716 (Labrus). 



J. & G., 484; M. V., 120; B. ( I, 16; J. & E., I, 1012; N., 36 (nigricans); J., 44 (palli- 

 dus); F. F., I. 3, 39 (pallidus); F., 67; L... 25. 



Length 15 to 18 inches; form as in last species, depth 2.9 to 3.2; greatest 

 width about % greatest depth; depth caudal peduncle 1.6 to 1.8 in its length. 

 Color of back and sides above rather dark green, growing lighter toward 

 axis, and everywhere obscurely mottled with darker in ill-defined blotches; 

 middle of side traversed by a dark streak (indistinct in old specimens), which 

 is formed of more or less irregular and discontinuous blotches of dark sage- 

 green; belly opaque greenish white, sometimes with a faint rosy tint; iris sooty 

 green with bronze luster and with a narrow inner rim of gold; fins pale olive- 

 buff, the dorsal and caudal darker than the others; anal opaque whitish 

 toward tip; young with the lateral band conspicuous and as a rule little 

 broken into spots, passing forward through eye to end of snout; caudal of 

 young specimens pale near base and outer margin, between which is a dark 

 band. Head 2.8 to 2.9; width of head 1.9 to 2.4; interorbital space convex, 

 3.5 to 4.3; eye 5.8 to 7.6; nose 3.5 to 4; mouth very large, maxillary reaching 

 past hinder margin of orbit, 1.9 to 2.1 in head; lower jaw rather more promi- 

 nently projecting than in M. dolomieu; gill-rakers long, 7 or 8 on lower limb 

 of arch, besides rudiments. Dorsal X (occasionally IX), 12-13, the spinous 

 separated from the soft portion by a very deep notch, the last spine scarcely 

 more than }4 length of fifth; longest spine about 4 in head; caudal lunate; 

 anal III (or II), 10-11 (or 12); ventrals half way to vent; pectorals short, 2 

 to 2.4 in head. Scales 8 or 9, 62-68, 14-18; lateral line complete or nearly 

 so; scales on cheeks in 9 or 10 rows. 



In marked contrast to the preceding species, the large- 

 mouthed black bass is distributed mainly along the principal 

 streams or the lower courses of their larger tributaries, but it 

 is not by any means confined to these, occurring in lower pro- 

 portion in the smaller streams as well. It is also more equally 

 distributed throughout the state than the small-mouthed bass, 

 and by passing freely into the lower Illinoisan glaciation illus- 

 trates its indifference to warm and muddy water. We have 

 found it relatively commoner, in our 211 collections, in the 

 southern part of the state than in the central, and somewhat 

 more so in central than in northern Illinois, the coefficients of 

 frequency being 1.23, .97 and .80 respectively. Our data show a 

 fairly equal distribution of this species throughout the various 

 situations open to it, the ratios for lowland and upland lakes, for 

 creeks, and the smaller rivers, being approximately equal, and 

 those for the larger rivers about half as large. 



