174 
Psyche 
[June 
Sierran specimens than for the coastal specimens (Fig. 28). Likewise, 
metatarsus IV is longer relative to metatarsus I than in most coastal 
specimens, but the overlap is greater. It is worth noting that the only 
two mature specimens collected low (2000 to 2500 ft.) in the western 
foothills of the Sierras are less different from the coastal populations 
than are most of the higher (6500 to 8000 ft.) Sierran specimens in 
some characters (see Figs. 27, 28). The only instance of striking 
intra-coastal geographic variation is the relatively long tibia I (and 
femur I) of sample A (Fig. 29). 
The ends of the AL spinnerets are sclerotized and lack spigots 
(Fig- 34 ) on all (20) Sierran females except for the two specimens 
collected lower in the western foothills ; these each possess a single 
spigot on each AL spinneret. All (66) coastal females but 9 have a 
single spigot on each AL spinneret (Fig. 33) ; 8 of these 9 have 
one “normal” AL spinneret and one like the higher Sierran females, 
the last (from B) lacks spigots on both. The AL to PM spinneret 
length ratio and the shape of the PM spinnerets vary geographically 
as in the male samples. 
The coastal populations appear to exhibit considerable intrapopu- 
lation as well as geographic variation in seminal receptacle form, so 
that all samples are connected by overlap. Many specimens examined 
resembled Figure 81. Some have less prominent bowls (Fig. 83), 
or are more stout ( Fig. 80) , or have a larger bowl diameter to stalk 
diameter ratio (Fig. 82). The Sierran specimens usually have rela- 
tively longer stalks and relatively narrower bowls (Figs. 84-86) than 
most coastal specimens, but there is some overlap. 
discussion. The patterns of geographic variation of a. number 
of characters indicate a considerable reduction of gene flow between 
the coastal population and the Sierran population. At present the 
Central Valley must be a formidable barrier to such gene flow, and 
there appears to be no contact between these populations in the 
more favorable montane environment to the north of the valley. It 
is, of course, necessary to assume that the Sierran population was 
once a part of (geographically continuous with and freely interbreed- 
ing with) the coastal population, possibly as recently as the more 
humid periods of the Pleistocene. 
The important problem is whether or not sufficient isolating mech- 
anisms have evolved since their separation to make these two pop- 
ulations different species. A comparison of the morphological 
distinctness of these two populations with the differences between any 
pairing of the very distinct and not too closely related species of 
