No. 4. — Diagnoses of new American Arachnida. By Ralph V. Chamberlin. The new arachnids in several collections submitted for identification are here diagnosed to render their names available for early use in connection with the ecological and other studies which led to the mak-ing of the collections. Of these collections mention may be made specially of one by Prof. W. C. Alice on Barro Colorado Island, Canal Zone, of one by James Zetek made in the course of work on the fauna of termite nests, also in the Canal Zone, and of one consisting of speci-mens taken from the stomachs of toads and the crops of birds in various parts of North America in the course of studies on food-habits made by the U. S. Biological Survey at Washington. The types of these new species are in the Museum of Comparative Zoology, Cambridge. ARANEINA. Ctenizidae. Pachylomerus eremus, sp. nov. 9 . Carapace and legs dusky brown, paler over a median area in front of the strongly procurved thoracic impression. Sternum, coxae of legs beneath, and the tarsi yellowish. Abdomen with a slightly purplish cast, the spinnerets light brown. Eyes on a slightly elevated tubercle. Area of median eyes wider behind than in front in the ratio 13:10. Anterior median eyes with diameter not half that of an anterior lateral. Inner margin of furrow of chelicera with four teeth, the outer with seven. Labium in type with the teeth in three series. Endites with teeth over entire length, those toward distal end smaller than the basal ones. Anterior tibiae and tarsi with a band of several series of spines along each side. Patellae I and II with an obtuse protuberance on caudal side, and patella I with a single spine at distal end on anterior side. Patella III with several short spines on anterior side of which the distal ones are larger than the others. Tibia III with a few small spines across distal end above and several stouter ones at distal end on caudal side. Metatarsus III with spines only on distal half above. Length, 8.5 mm. Type.— M. C. Z. 1,261. Locality. — Barro Colorado Island. One female.