PERCIXA LOG-PERCHES 281 



camurum and Boleichthys fusiformis, which occur in similar 

 waters, and most abundantly also in the same part of the state. 

 In these two common species the coefficient of association each 

 with the other is unusually high, much higher, indeed, than the 

 average coefficient for the most typical species of the subfamily. 



The darters are distributed through southern Canada and 

 the United States east of the Rocky Mountains and northern 

 Mexico; as far westward as south Nebraska; and northward to 

 Qu'Appelle, in the basin of the Red River of the North. There 

 are some eighty or ninety species of this subfamily in North 

 America, and in Illinois twenty-three species belonging to ten 

 genera. The majority of them are less than four inches long, 

 and one of them does not exceed an inch and a half. The name 

 of "darter" is given them because of their quick, swift flights 

 through the water, a fact which also suggested to Rafinesque 

 the technical name of one of the early genera described by him 

 Boleosoma, meaning dart-body. To the fisherman and the 

 ordinary observer these little percoids are usually either wholly 

 unknown or go by the general name of minnow, or, perhaps, by 

 the more appropriate one of " perch minnow." They are, as a 

 rule, brilliantly colored, and sexual color-differences are strongly 

 marked in many species, the females being duller than the males. 



The species are much subject to local variation, but they are 

 nevertheless commonly well marked, and the local forms can 

 usually be referred, without much difficulty, to the specific 

 group. All spawn in spring, so far as known. 



GENUS PERCINA HALDEMAN 



LOG-PERCHES 



Body elongate, sybcylindrical ; mouth small and inferior; premaxillaries 

 not protractile; teeth on vomer and palatines; belly with a median row of 

 enlarged caducous plates; vertebrae (P. caprodes} 44 (23 + 21); pyloric caeca 

 (P. caprodes) 6; pseudobranchiae present, rudimentary. In the diagnostic 

 features above noted this genus is scarcely different from Hadropterus. On 

 the cranial characters of Percina, which in its skull structure more closely 

 resembles Perca than do the other etheostomids, Jordan and Eigenmann 

 have said: "As compared with the other darters, the skull of Percina is 

 much broader between the eyes; the parietal bones are more strongly ridged, 

 the sutures more distinct, the top of the cranium beyond the eyes more de- 

 pressed, and the supraoccipital crest more developed than in most of the 

 others. "* The largest of the darters ; coloration olivaceous, with dark vertical 

 bands on body, more or less broken into spots and reticulations; species 2. 



* Proc. TT. S. Nat. Mus., Vol. 8, p. 68. 

 27 F 



