84 BULLETIN 168, UNITED STATES NATIONAL MUSEUM 



Isotoma denticulata Schaffer, 1896, p. 189. — Poppe and Schaffer, 1897, p. 



268.— Carl, 1899, p. 321.— Borner, 1901a, p. 57.— Krausbauer, 1902, 



p. 43.— ScHiLLE, 1906, p. 8. 

 Isotoma syno7iymica MacGillivray, 1896, p. 52. 

 Isotoma terminata MacGillivray, 1896, p. 56. 

 Isotoma (Vertagopus) arborea Collinge, 1910, p. 9. — Womersley, 1924a, p. 32; 



1927, p. 376. 

 Vertagopus arborea Stach, 1922a, p. 19. — Handschin, 1929, p. 65. 



Description. — Blacldsh purple, dorsally mottled with small unpig- 

 mented spots, which are round, oval, or elongate. Legs and furcula 

 whitish or yellowish, except coxae and manubrium, which are usually 

 pigmented. Antennae purplish. Young individuals are brown 

 (Schaffer). Eyes (pi. 28, fig. 309) eight on each side, unequal, the 

 two inner proximal eyes of each group being smaller than the others. 

 Postantennal organ (pi. 28, fig. 309) elliptical to suboval, one to two 

 times as long as the diameter of an adjacent eye. Antennae one and 

 one-third times as long as the head; segments in relative lengths 

 about as 5:9:7:13. or 5:9:8:16; second and third segments each with 

 a short incomplete apical subsegment. Sense organ of third antennal 

 segment (pi. 28, fig. 310) with a pair of subclavate sense rods, more 

 or less curving (see beyond), under a thin integumentary fold. Fourth 

 antennal segment without special olfactory setae; with a hemispherical 

 apical papilla and an adjacent bluntly conical peg. Unguis (pi. 28, 

 fig. 311) stout, curving, unidentate near the middle, or a little beyond 

 the middle, of the inner margin; with a pair of small lateral teeth 

 one-third from the base. Unguiculus one-half as long as the unguis, 

 extending three-fifths as far as the latter, broadly lanceolate, with 

 inner margin dilated and unidentate. Tenent hairs 2, 3, 3. Genital 

 and anal segments not ankylosed as a rule (see beyond). Third 

 abdominal segment equal to, or slightly longer than, the fourth (as 

 12:11). Furcula appended to the fifth abdominal segment and attain- 

 ing the ventral tube. Dentes from two to two and one-half times as 

 long as the manubrium, slender, gradually tapering, with numerous 

 dorsal crenulations, and convergent. Mucro (pi. 28, figs. 312-315) 

 shorter than hind unguiculus, quadridentate ; apical tooth hooked, 

 typically much shorter than the second tooth (pi. 28, fig. 312), but 

 in specimens from the United States often becoming almost as large 

 as the anteapical tooth; second tooth the largest, suberect or inchned 

 slightly backward; third tooth a httle smaller than the second, in- 

 clined backward or suberect; first three teeth in longitudinal aline- 

 ment; fourth tooth lateral, more proximal than the tliird tooth or 

 almost opposite the latter, inclined backward, sometimes reduced or 

 absent (pi. 28, fig. 315). Rami of tenaculum quadridentate; corpus 

 with several (as many as nine) setae. General clotliing of short dense 

 curving simple setae. Erect sensory setae occur in a transverse row 

 across the middle of each of the first four abdominal segments, on 

 the mesonotum anteriorly and posteriorly, and on the legs. The 



