Color in alcohol. Carapace: generally reddish brown, with eyes on black spots; numerous slender white hairs, especially around dorsal margin; interocular space with many subchitinous granules of white guanin making this region light colored with two dark colored spots near center. Chelicerae reddish brown. Maxillae and lip brown with whitish tips. Sternum light brown. Legs: first pair brown, with tarsi and prolateral surfaces of femora dark brown and metatarsi yellowish white; other legs similar with variations. Abdomen: region of weakly developed scutum reddish brown with two pairs of sigilla near center; just behind scutum is a transverse band of numerous yellowish white granules of guanin and in posterior quarter several obscure light and dark alternate chevrons; lateral sides brown with yellowish dots; venter dark brown with two rows of yellowish dots near center.
Female. A female which is probably immature is the only specimen of this sex available. The description of the allotype is, therefore, deferred until more material is available. The retromargin of the fang groove in this female shows three separate teeth.
Type locality. Male holotype from the C. Z. Forest Reserve, C. Z., Aug., 1939. One male paratype and the immature female from the Canal Zone Biological Area, July, 1939.
Genus Zygoballus Peckham, 1885
The Peckhams had a single female from Panama for which they made the genus Messua. Simon transferred the genus to Zygoballus. Professor Petrunkevitch had two females upon which he based the description of Z. maculatipes. Mr. Banks identified a female as Z. rufipes Peckham, but I believe this specimen to belong to Z. optatus sp. nov. Mr. Banks also identified an immature female as Z. tibialis F. Cambridge. This specimen is impossible to place with certainty but it probably belongs to one of the new species described in this paper. I conclude, therefore, that at the present time four species of Zygoballus are known from Panama, two of them only from females.
Key to the species of Zygoballus from Panama
Males
1. Palpal tibial apophysis slender, fully half as long as bulb; embolus long and slender, fully half as long as bulb. . . . . Z. optatus, (p. 410)
1. Palpal tibial apophysis short and robust, about one third as long as bulb; embolus about one third as long as bulb. . . . . Z. electus, (p. 405)
