Virginia Ictalurid Catfishes 85 
Fig. 2. Relationship of eye length (as % SL) to SL in Virginia Ictalurus (Amiurus) 
with emarginate caudal fins. 
typical bullheads group. The flathead bullheads are best distinguished 
from other bullheads by the presence of a large dark basal blotch, its up- 
per edge straight or convexly rounded, in the dorsal fin (Fig. 3D). The 
blotch was also recognized as a key character and figured for /. 
platycephalus by Eddy (1969), and depicted for /. brunneus by Smith- 
Vaniz (1968). Eye size is secondarily useful in separating the groups, the 
size being moderate in flatheads and small in typical bullheads. Although 
size varies allometrically relative to SL, more pronouncedly in small 
juveniles (Fig. 2), the differences between the groups are generally ob- 
vious, with little overlap when comparing specimens of similar lengths. 
The third member of the flathead bullhead group, /. serracanthus, a 
primarily Floridean species, also has the dorsal blotch and moderate eye 
size character states (figure and description in Yerger and Relyea 1968). 
Head shape of flathead and typical bullheads is variable, from essentially 
flat to slightly convex dorsally in flatheads, versus usually more elevated 
or markedly convex in typical bullheads. Overlap in head shape and eye 
size is such that sole reliance on either character for group separation will 
result in some misidentifications. 
Ictalurus brunneus and /. platycephalus are best distinguished from 
each other by barbel pigmentation and premaxillary teeth configuration, 
and secondarily by meristics. Most juveniles and adults of I. brunneus 
examined had profusely dark pigmented mental (chin) barbels, whereas 
most specimens of /. platycephalus had unpigmented or slightly pigmen- 
ted, pale mental barbels. The absence of profusely developed mental bar- 
bel pigment in /. brunneus usually occurs in specimens smaller than 100 
mm SL. In I. platycephalus the presence of slightly pigmented mental bar- 
bels occurs mostly in adults, particularly in the lateral pair of barbels; the 
