BULLETIN FLORIDA STATE MUSEUM


tributaries of the Mississippi River in eastern Arkansas and Missouri.
 Apparently absent from western Tennessee west of the Tennessee
River system, although it is quite common throughout most of the
Tennessee drainage itself in Tennessee, extreme northeastern Missis-
sippi, northern Alabama, northwestern Georgia and southwestern Vir-
ginia. It has not yet been reported from North Carolina.
 To the north it is one of the most abundant cyprinids in the Ohio
River system, except for the upper Kanawha (New) River drainage,
where it is practically absent-the single record for this drainage
(USNM 177878) is believed an introduction.
 Common in tributaries of the Gasconade and Meramec rivers
in Missouri, it is rare in the Osage drainage of that state. It is found
in some of the smaller tributaries of the Mississippi River in eastern
Missouri both north and south of the Missouri River, and occurs in a
few scattered localities in northeastern Missouri. There are as yet
no records for Iowa. It is common in the Illinois River system in
Illinois and in suitable habitats of the more eastern and southern
parts of the state, but it has not yet been found west of the Illinois
drainage.
 It occurs throughout most of the lower Great Lakes region and
is entirely absent only from the Lake Superior drainage. Its appar-
ent absence from the more northern tributaries of the other Great
Lakes seems to be related primarily to temperature, as its northern dis-
tributional limit coincides closely with the 70'F July isotherm (Rad-
forth, 1944: 89). In the Lake Michigan basin it is known from ex-
treme southeastern Wisconsin, northeastern Illinois, northern Indiana,
and from western Michigan. It occurs sparingly in the Lake Huron
basin, having been recorded only from certain tributaries of Saginaw
Bay in Michigan and from a few localities in Ontario. It is wide-
spread and common throughout most of the Lake Erie drainage. In
the Lake Ontario basin its occurrence is spotty, with all known records
coming from streams flowing into the south side of the lake.
 The lack of records from any streams draining into the Atlantic
Ocean indicates that this species probably was a late entrant into the
Great Lakes drainage and failed to reach the Horseheads Outlet into
the upper Susquehanna River system (Bailey, 1945: 125-126) before
this connection was eliminated.
 In recent times N. chrysocephalus seems to have replaced the
closely related N. cornutus throughout much of the latter's former
range. This is substantiated by the presence of isolated populations
of cornutus in West Virginia and Indiana, and by Trautman's (1957)
observations over the past 35 years on the relative distribution of


Vol. 8