BULLETIN FLORIDA STATE MUSEUM


CHASMODES BOSQUIANUS ...................... ...........................71
CHASMODES BOSQUIANUS BOSQUIANUS ................................72
CHASMODES BOSQUIANUS LONGIMAXILLA new subspecies ..................85
CHASMODES SABURRAE............. ... ... ............................91
ZOOGEOGRAPHY .............................................................95
EXPERIMENTAL HYBRIDIZATION ...........................................96
SUM MARY ................................................. .................97
LITERATURE CITED ................ .................... ................. 97

 INTRODUCTION
 Chasmodes Valenciennes 1836 is a ditypic genus commonly encoun-
tered in bays and estuaries from Chesapeake Bay, Maryland, around the
southern tip of Florida, and westward to Veracruz, Mexico. Although the
species are usually found in salinities ranging from 15 to 25 ppt, one has
been recorded from salinities as low as 5.5 ppt in Whitewater Bay, Florida
(Springer 1959), and can survive salinities in excess of 35 ppt. They are
usually found in grassbeds or over hard substrates permeated with small
holes and crevices (such as oyster reefs and rock jetties) and have occasion-
ally been collected over open mud or sand bottom (Springer 1959).
 Springer (1959) reviewed the genus, but subsequent workers have
experienced difficulty identifying specimens. The mandibular tooth and
maxillary length characters Springer used permit identification of most
adult specimens, but do not always provide a distinct separation when
applied to young individuals or specimens from the eastern coast of Flor-
ida. My study describes several characters not discussed by Springer,
which permit specific identification of any postlarval specimen of Chas-
modes regardless of locality and presents a key to species and subspecies.
Springer recognized the distinctness of the two species in the area of
sympatry in the northern Gulf of Mexico, but offered no explanation for
this phenomenon. A mechanism is proposed herein to explain how genetic
integrity of the two species is maintained within this area. Springer's
observation on the divergence of the Texas population of C. bosquianus is
supported and, in addition, the northern Gulf of Mexico population is
recognized as a distinct subspecies. Analysis of the Everglades population
supports Springer's contention that this population is not taxonomically
distinct from neighboring populations.
 The two species of Chasmodes are of special interest from a zoogeo-
graphic point of view. Their distribution patterns coincide with those
described for other fishes (e.g. Dawson 1964, Relyea 1965, Shipp and
Yerger 1969, Hardy 1980) and help to define previously proposed faunal
transition areas. In order to elucidate the zoogeographical implications of
the distribution patterns, the evolutionary histories of the species are ana-
lyzed using geological and climatological evidence.
 Since the original description of the genus Chasmodes in 1836, the only


VOL. 29, NO. 2