THE AMERICAN SPIDER GENERA 
SPINTHARUS AND THW AITESI A 
(ARANEAE: THERIDIIDAE)* 
By Herbert W. Levi 
Museum of Comparative Zoology, Harvard University 
The two genera Spintharus and Thwaitesia are very similar. I 
have not combined them, however, because I expect that additional 
species may throw new light on the relationship. Both genera are 
close to Episinus in genitalic structure, general appearance, and in 
possession of a small spigot at the anterior pair of spinnerets (Levi 
and Levi, 1962). 
Thwaitesia has never been revised. North American Spintharus 
has previously been revised (Levi, 1955). On reexamining a few 
specimens, I began to think that I had confused several species in 
my previous revision and that the specimens could easily be sorted 
cut into three species. Reexamination of larger collections, how- 
ever, reestablished my previous observation that the genitalia of 
Spintharus are variable and that there are at most two species. Evi- 
dence for this is presented in Figures 1 and 2. 
A National Science Foundation Grant (G-4317) permitted the 
examination of many types, a grant from the National Institutes of 
Health (AI-01944) supported the research. I am thankful to the 
following colleagues who provided me with specimens or permitted 
examination of types under their care: Dr. W. J. Gertsch of the 
American Museum of Natural History (AMNH), Dr. H. Exline 
(Mrs. D. Frizzell) for specimens of her own collection and, with 
Dr. E. S. Ross, specimens from the California Academy of Sciences 
(CAS). Dr. J. Cooreman and J. Kekenbosch of the Institut Royal 
des Sciences Naturelles de Belgique (ISNB), Dr. A. M. Chickering 
whose collections are housed in the Museum of Comparative Zoology, 
Dr. G. Owen Evans, K. Hyatt, E. Browning of the British Museum 
(Natural History) ; Prof. M. Vachon of the Museum National 
d’Histoire Naturelle, Paris (MNHN), Prof. G. C. Varley and E. 
Taylor of the Hope Department of Entomology, Oxford, and Dr. O. 
Kraus of the Senckenberg Museum, Frankfurt (SMF). 
Spintharus Hentz 
Spintharus Hentz, 1850, Jour. Boston Soc. Nat. Hist., 6: 284. Type species 
by monotypy: Spintharus flavidus Hentz. 
*Manuscript received by the editor April 29, 1963. 
223 
