54 BULLETIN 168, UNITED STATES NATIONAL MUSEUM 



PROISOTOMA (PROISOTOMA) SEPULCRALIS (Folsom) 



Plate 20, Figures 208-215 



Isotoma sepulcralis Folsom, 1902b, p. 364. 



Description. — White; sometimes slightly pigmented with minute 

 scattered round black spots. Eye spots black. Eyes (pi. 20, fig. 208) 

 five on each side, equal; occasionally four on each side. Postantennal 

 organ (pi. 20, fig. 208) distant from eyes, elliptical, oval or ovate, 

 twice as long as the diameter of an eye. Antennae subequal to the 

 head in length ; segments stout, in relative lengths about as 6 : 10 : 9 : 19. 

 Sense organ of third antennal segment (pi. 20, fig. 209) with a pair 

 of subcylindrical or subclavate feebly curving rods, subtended by a 

 weak cuticular ridge. Fourth antennal segment with terminal 

 tubercle, subapical papilla, and slender curving olfactory setae. 

 Abdominal segments normally without ankylosis. Anus ventro- 

 caudal. Femur and tibiotarsus each with a distal subsegment. 

 Unguis (pi. 20, fig. 210) simple, untoothed. Unguiculus extending 

 two-thirds as far as unguis, on hind feet, ovate-lanceolate, acute, 

 untoothed. Front claws smallest, the other pairs successively larger. 

 Tenent haks absent ; instead, a long simple seta. Fourth abdominal 

 segment one-third longer than the third segment, and bearing the 

 furcula. Furcula short, extending as far as the posterior margin of 

 the second abdominal segment. Manubrium stout, with a pair of 

 stout ventral subapical setae and several smaller dorsal setae. Dens 

 stout, narrowing distally, two-thirds as long as manubrium, with 

 eight to ten coarse, rather irregular, oblique, dorsal crenulations, and 

 six ventral setae. Mucrones (pi. 20, figs. 211-214) one-third as long 

 as dens, slightly longer than hind unguiculus, elongate, subequally 

 tridentate; apical tooth sharp, feebly hooked or, rarely, falcate; sec- 

 ond tooth conical, erect; third tooth slightly smaller than the second, 

 erect or feebly inclined, lateral in position. The mucro is narrowly 

 bilamellate: An inner lamella extends from the base of the mucro 

 to the anteapical tooth, and an outer lamella from the base to the 

 third (or lateral) tooth. Rami of tenaculum (pi. 20, fig. 215) quadri- 

 dentate; corpus with a single strong curving ventral seta. Clothing 

 of numerous short stiff simple setae, absent on the anterior and pos- 

 terior parts of most of the body segments; with longer erect simple 

 sensory setae. Integument smooth. Maximum length, 1.8 mm. 



Remarks. — In an occasional individual the genital and anal seg- 

 ments are ankylosed without suture. 



The mucrones vary considerably in minor details, as shown in 

 plate 20, figures 211-213. In one case, the third tooth was absent 

 on the left mucro but present on the right one ; and in a single instance 

 (among more than 5,000 individuals) each mucro had a proximal 

 fourth tooth (pi. 20, fig. 214). 



