BULLETIN FLORIDA STATE MUSEUM


 1950: 165, 167; Taylor, 1954: 43; Trautman, 1948: 171 [in part]; Trautman,
 1957: 114-115 [in part])
Notropis cornutus X Semotilus atromaculatus (Bailey and Oliver, 1939: 172;
 Greeley, 1938: 51-52; Koster, 1939:207; Raney, 1940a: 7; Raney, 1940c:
 135; Simon, 1946: 91; Taylor, 1954: 42)
Notropis cornutus X Semotilus corporalis (Bailey, 1938: 150-151; Greeley, 1938:
 52; Raney, 1940a: 7)
Notropis pilsbryi X Dionda nubila (Moore and Paden, 1950: 92)
Notropis pilsbryi X Notropis rubellus (Cross, 1954: 313; Moore and Paden,
 1950: 92)

 ZOOGEOGRAPHY AND PHYLOGENY

 The zo6geographic and phylogenetic history of a group of animals,
often the subject of speculation, is usually reconstructed only with
difficulty. Because the genus Notropis has evolved so recently, most
of the forms linking the included natural groups are still extant and
allow a relatively clear interpretation of the phylogenetic relation-
ships. On the other hand, the high degree of speciation in the genus
makes the zo6geographical relationships extremely complex.
 The subgenus Luxilus probably evolved in the Mississippi basin,
perhaps during the early to middle Pliocene. This hypothesis is
based first on the present geographical distribution of the Luxilus
complex and, second, on the assumption of a Miocene invasion of
North America by the family Cyprinidae (Romer, 1945: 583).
 The primary division within the subgenus most likely involved
the precursor of Notropis coccogenis and Notropis zonistius. Judging
from its present distribution, the coccogenis group probably evolved
in the Tennessee River system. The marked differentiation of cocco-
genis and zonistius from the other species of Luxilus indicates that
isolation from stocks in the Mississippi Valley lasted for a consider-
able time. The reasons for isolation, however, are unknown at pres-
ent. Later, presumably still during the Pliocene, a segment of this
stock reached the Chattahoochee River basin, there evolving into
N. zonistius, while the stock remaining in the Tennessee system gave
rise to N. coccogenis. Presumably this transfer was effected through
a localized stream capture rather than by direct connection of the
Chattahoochee with the Tennessee. No evidence indicates such a
connection, and these river systems show little close faunal similarity.
 Also during the Pliocene another segment of the Mississippi Val-
ley stock presumably became isolated in the Ozark region. This
eventually gave rise to the zonatus group, which includes Notropis


Vol. 8