158 
Psyche 
[June 
by a grant from the Evolutionary Biology Committee of the Depart- 
ment of Biology, Harvard University. 
Methods 
Statistical methods. An analysis of variation of quantitative char- 
acters was performed on the three species of Atypoides with two 
aims in mind : to discover quantitative characters of value in dis- 
tinguishing between species of antrodiaetids, and to investigate in a 
preliminary manner the geographic variation within each species. 
There is greater need for such studies in mygalomorph spider tax- 
onomy than in many araneomorph groups because of the lack of 
diagnostically useful complex external genitalia in the former. How- 
ever two major difficulties confront anyone attempting to study 
variation in mygalomorph species: the difficulty of collecting samples 
of adequate size, and the more difficult problem of achieving age 
homogeneity within samples of females. Antrodiaetid females (and 
females of other mygalomorph species) live and continue to molt 
for one to several years after becoming sexually mature. No external 
structure or characteristic gross difference in seminal receptacle form 
has been found which indicates when a female has reached sexual 
maturity or what instar an adult female may be. 
In the present study a female specimen was included in a popu- 
lation sample only if it had a longer carapace than the smallest 
reproductively active female (with an abdomen swollen with eggs 
or with brood in her burrow) from the entire sample of specimens 
of that species. An exception was made for A. riversi where the 
smallest of a large number of reproductively active females collected 
in the coastal population was considerably larger than the single 
reproductively active Sierran population sample female. The low 
size limit for each of these two major population samples was there- 
fore determined by the smallest reproductively active female within 
it. The non-reproductively active females included in a sample rep- 
resent first adult instar females collected in the summer just before 
or after their initial mating, later adult instar females without 
broods, and probably an occasional immature female. It is likely 
that the small number of reproductively active females (one each) 
collected in the Sierran samples of A. riversi and in Atypoides 
gertschi result in samples somewhat biased toward the upper end of 
the actual adult female body size range. 
Twenty-one measurements and 13 meristic characters were re- 
corded for 60 males and 159 females of the three species. (The 
abbreviations and definitions for these measurements and meristic 
