528 Percoidea, or Perch-like Fishes 
nigrum, the Johnny darter in the West, and Boleosoma olmstedi 
in the East are among the commonest species, found half hid- 
den in the weeds of small brooks, and showing no bright colors, 
although the male in the spring has the head, and often the 
whole body, jet black. 
Crystallaria asprella, a large species almost transparent, 
is occasionally taken in swift currents along the limestone 
Fic. 417.—Crystal Darter, Crystallaria asprella (Jordan). Wabash River. 
banks of the Mississippi. Still more transparent is the small 
sand-darter, Ammocrypta pellucida, which lives in the clearest 
of waters, concealing itself by plunging into the sand. Its 
scales are scantily developed, as befits a fish that chooses this 
Fie, 418. —Sand-darter, Ammocrypta clara (Jordan & Meek). Des Moines River. 
method of protection, and in the related Ammocrypta beant of 
the streams of the Louisiana pine-woods, the body is almost 
naked, as also in Joa vitrea, the glassy darter of the pine-woods 
of North Carolina. 
In the other darters the body is more compressed, the move- 
ments less active, the coloration even more brilliant in the 
males, which are far more showy than their dull olivaceous 
mates. 
To Etheostoma nearly half of the species belong, and they 
