1972] 
Brady - — So sip pus 
3 
contrasting sharply with the black background of the carapace (Figs. 
34-38), and a peculiar epigynum (Figs. 10-13, 19-24). 
At Lake Lochloosa we encountered a population with a predomi- 
nant 4-4 tooth pattern (Table 1), but with an unusual and some- 
what variable epigynal structure (Figs. 14-18), and a, more diffuse 
color pattern than S. floridanus, the white or yellowish markings on 
the carapace not contrasting sharply with the black background of 
the carapace (Figs. 40-41). The available data below indicate that 
this is a distinct population and it is recognized here as S. janus. 
At Lake Placid, in south central Florida, we made our most in- 
teresting discovery. Here we found a population of large specimens, 
unique in color pattern (Fig 39), epigynal structure (Figs. 25-27), 
and with 3-3 posterior cheliceral teeth (Table 1). This population 
is designated S. placidus and described below. 
From the investigation made in 1968 and information gathered 
since, it is evident that there are populations of Sosippus in penin- 
sular Florida that are quite different from mimus and floridanus . 
The distribution patterns of different populations of Sosippus in 
Florida appear to reflect recent geologic events. Sosippus placidus 
is restricted to an area represented by Red Hill Island of the Afto- 
nian Interglacial (Laessle, 1958). 
The rise in sea-level during the Pleistocene with the concomitant 
production of various islands where the Florida peninsula now stands 
has influenced speciation in at least three different genera of spiders. 
The influence of Pleistocene events is seen in the distribution pat- 
terns of certain species of Geolycosa (McCrone, 1963), Latrodectus 
(McCrone and Levi, 1964), and Sosippus (Map 1). In consider- 
ing the series of events producing differentiation in these spiders, 
several factors need to be emphasized. First it would seem that salt- 
water currents served as an effective barrier to gene flow so that 
divergence of the populations could proceed. I think that these bar- 
riers, by themselves, would be insufficient to account for the re- 
productive isolation of these populations. Even where the spiders 
have limited dispersal powers (as in Geolycosa) other factors must 
have been in operation. I suggest that the reduction of population 
numbers *on the Pleistocene islands with a corresponding reduction 
in genetic variability played a significant role in the process of specia- 
tion. These geographical isolates became genetically homogeneous 
and ecologically specialized for the xerophytic conditions of the 
Pleistocene islands. Even today the limits of the species ranges of 
these spiders is prescribed by the extent of the xeric communities 
