COLLEMBOLA OF THE FAMILY ISOTOMIDAE 89 



ISOTOMA (ISOTOMA) DIFFICILIS, new species 



Plate 28, Figures 320-323 



Description. — White, minutely spotted with black. Eye patches 

 small and irregular. Eyes (pi. 28, fig. 320) eight on each side, equal. 

 Postantennal organ (pi. 28, fig. 320) elongate, about as wide as the 

 diameter of an eye, and five to seven times as long. Antennae longer 

 than the head (as 4:3), with segments in relative lengths about as 

 6:9:10:15; first segment cylindrical; second subclavate, third clavate, 

 fourth elliptical. Sense organ of third antennal segment with a pair 

 of linear unprotected rods; fourth antennal segment without special 

 olfactory setae. Third and fourth abdominal segments subequal in 

 length. Genital and anal segments not ankylosed. Unguis (pi. 28, 

 fig. 321) with a pair of small lateral teeth, and a strong tooth behind 

 the middle of the inner margin. Unguiculus extending two-thirds 

 as far as unguis on the hind feet, and half as far on the other feet, 

 ovate, acuminate, unidentate. Tenent hairs absent. Furcula ex- 

 tending to the ventral tube. Manubrium short and stout, v/ith many 

 stift" setae dorsally and ventrally. Dentes three times as long as 

 manubrium, slender, tapering, finely crenulate dorsally, with a few 

 stiff setae dorsally and dense setae ventrally. Mucro (pi. 28, figs. 

 322, 323) about as long as hind unguiculus, tridentate; apical tooth 

 long and hooked; anteapical smaller, conical, erect; third tooth lateral, 

 oblique, large, almost straight or feebly hooked, Mucro in lateral 

 aspect strongly rounded ventrally. Rami of tenaculum quadriden- 

 tate; corpus with nine or ten setae. General clothing of dense short 

 stiff setae. The outstanding sensory setae become very long on the 

 posterior part of the abdomen, with a few spinules on the convex 

 surface. Integument smooth. Length, 1.5 mm. 



The number and position of the eyes were difficult to make out, by 

 the method of depigmentation, but plate 28, figure 320, composed 

 from studies of 10 individuals, is essentially correct. 



Cotypes.—\J.S.l<iM. no. 42975. 



Distribution. — Recorded as follows: 

 Illinois: Urbana, February 23, in the leaf stratum of a forest, I. H. Blake. 



ISOTOMA (ISOTOMA) MARISSA. new species 



Plate 29, Figures 324-330 



Description. — A stout species. General color bluish. White, 

 mottled with purple pigment, and broadly banded with blackish 

 purple. The broad transverse bands occur on the posterior border 

 of the head and along the posterior borders of all the body segments 

 except the prothorax and the genital and anal segments. Antennae 

 mottled with purple; first three segments heavily pigmented apically. 



