HADROPTERUS BLACK-SIDED DARTERS 285 



HADROPTERUS PHOXOCEPHALUS (Nelson) 



Nelson, 1876, Bull 111. State Lab. Xat. Hist., I 1, 35 (Etheostoma) 



1 & G . 501 (Alvordius); M. V., 127 (Etheostoma); B . I, 63 (Percina); |. & E.. 



I. 1030; J . 39 (Alvordius): P., 65; L , 27. 



Length 3 inches; body moderately elongate and compressed; form 

 distinctive among darters for its graceful outlines, the back gentlv 

 elevated and the anterior portion of the body faultlessly tapered to the 

 end of the slender pointed head; depth 5.4 to 6.2 in length; greatest 

 width of body about | of its depth ; depth caudal peduncle 1 . 8 to 2.4 in 

 its length. Color yellowish brown, more or less marbled, blotched, and 

 tessellated with darker, but the colors generally duller than in H. aspro; 

 sides with about 12 or 13 more or less indefinite dusky blotches, some- 

 times confluent into a moniliform band, in instances fading so as to be- 

 come almost imperceptible; back with tessellations and upper portion 

 of sides with marblings of dark color, ordinary examples having a vermic- 

 ulated appearance; first dorsal with a broad band of orange-red across 

 its middle and with a narrow outer edging of pale blue, the hues much 

 more brilliant in males than in females; second dorsal and caudal faintly 

 barred; other fins plain, the anal and ventrals duskv in males; a dark 

 band from front of orbit through nostril to end of snout; vertical streak 

 below eye faint. Head long, slender and quite pointed, 3.6 to 3.9 in 

 length ; width of head 2 . 1 to 2.4; interorbital space extremelv narrow, 6 . 7 

 to 7.9 in head; eye 3.8 to 4.5; nose pointed, 3 . 5 to 4 in head; mouth 

 moderate, maxillary reaching a little past front of orbit, the cleft 3 . 4 to 4 

 in head ; jaws nearly equal ; gill-membranes free from isthmus and broadly 

 connected, the distance from muzzle to their free posterior margin 1$ to 

 H times that to back of orbit. Dorsal fin XII or XIII, 12-14; spinous 

 and soft portions scarcely separated at base; height of first dorsal 2 . 2 to 



2 . 9 in head, second 1 . 7 to 2 . 1 (height of first 70 to 88 per cent, of second) ; 

 caudal slightly emarginate; anal II, 8 or 9, rarely 10 or 11; pectorals 1 . 2 

 to 1.4 in head; separation of ventrals slightlv less than their width at 

 base. Scales 8-10, 64-69, 10-12 [12-18]; usually no pores lacking; cheeks 

 covered with very fine scales, in 14 or 15 rows; opercles and nape scaled ; 

 breast naked or with a median large caducous shield; mid-ventral line 

 with small caducous plates. 



This modestly colored but shapely darter is distributed much like 

 Percina caprodes, except that we have not found it in the northern 

 glacial lakes, and that it is dispersed more widely through the smaller 

 streams. It has occurred in ninety-five of our collections, most 

 abundantly in the Illinois basin, but frequently also in the Rock 

 River and its tributaries. It is commonest in northern Illinois and is 

 least frequently found in the southern part of the state. Like Per- 

 cina caprodes, it has been taken by us most generally from the smaller 

 rivers (3.39) and from creeks (1 .59), but only rarely from the largest 

 rivers (.4) or from lakes or sloughs (.2). It is preeminently a species 

 of swift water with a bottom of rock or sand, 94 per cent, of our o '1 



