COLLEMBOLA OF THE FAMILY ISOTOMIDAE 63 



General clothing of rather dense short simple setae, becoming con- 

 siderably longer on the anogenital segment. Outstanding sensory 

 setae simple, short and stiff, much longer on the ano-genital segment. 

 Integument smooth. Maximum length, 1.1 mm. 



Remarks. — This species agrees in most respects with the European 

 species tenella Renter, types of which were redescribed by Linnaniemi 

 (1912). In tenella there is, however, no ankylosis of the genital and 

 anal segments; the unguiculus is narrow; the dorsal folds of the dens 

 are present apparently as far as the mucro ; and the latter is relatively 

 slender and not strongly rounded ventrally. 



Tliis species may prove to be synonymous with Isotomina ther- 

 mophila var. anomala, for it differs only in minor respects from the 

 description and figures of that form as given by Linnaniemi (1912, p. 

 136). 



Cotypes.—V. S.'N.M. no. 42984. 



Distribution. — Recorded as follows: 



Illinois: Homer, April 23, 24, and 29, under boards on grass. 



PROISOTOMA (PROISOTOMA) IMMERSA (Folsom) 



Plate 24, Figures 262-268 



Isotoma immersa Folsom, 1924, p. 1. 



Description. — Ground color pale yellow in alcohol (possibly white 

 in life); pigment purple, becoming blackish where dense. Head and 

 body coarsely mottled with irregular spots dorsally; body segments 

 bordered posteriorly with broad bands of blackish. First three 

 antennal segments each with an apical band; fourth segment dark 

 apically. Legs pale yellow, the segments mottled with more or less 

 pigment. Furcula and ventral region unpigmented. Head (pi. 24, 

 fig. 262) large in proportion to the body, and two-fifths as long as the 

 latter. A blackish A-shaped mark extends forward from the eyes. 

 Eyes (pi. 24, fig. 263) eight on each side, unequal. Postantennal 

 organ (pi. 24, fig. 263) close to eyes, elliptical to oval, usually con- 

 stricted at the middle, and two to three times as long as the diameter 

 of an adjacent eye. Antennae stout, approximate, subequal to, or 

 slightly longer than, the head, with segments in relative lengths about 

 as 11:14:22:45. Antennal segments strongly telescopic (pi. 24, fig. 

 264). Basal antennal segment cup-shaped, immersed in a pit (pi. 24, 

 fig. 262); second subcylindrical ; third subclavate; fourth elliptical. 

 Sense organ of third antennal segment (pi. 24, fig. 265) with a pair of 

 feebly curving rods subtended by a chitinous ridge. Fourth antennal 

 segment without special olfactory setae. Prothorax concealed from 

 above by the head and mesonotum. Abdominal segments without 

 ankylosis. Body segments (excepting prothorax) in relative lengths 

 about as 10:6:4:5:6:8:5:4. Fourth abdominal segment longer than 

 the third (as 2:1 or 3:2). Anal segment relatively long and broad; 



