MICROPTERUS BLACK BASS 267 



MICROPTERUS SALMOIDES (Lacepede) 

 (large-mouthed black bass) 



Lac^pMe, 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 IS to 18 inches ; form as in last species, depth 2 . 9 to 3 . 2 ; great- 

 est width about f 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 S . 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 prominently projecting 

 than in M. dolomieu ; gill-rakers long, 7 or 8 On lower limb of arch, be- 

 sides rudiments. Dorsal X (occasionally IX), 12-13, the spinous sep- 

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

 scarcely more than J 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 proportion 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 illustrates its indifference to warm and 

 muddy water. We have found it relatively commoner, in our 211 col- 

 lections, 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 situa- 

 tions 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. 



