38 BULLETIN 168, UNITED STATES NATIONAL MUSEUM 



disturbed they prefer not to jump, aud are not particularly strong 

 leapers when they do" (Guthrie). 



Through the courtesy of Profs. II. F. Nachtrieb and J. E. Guthrie 

 I obtained for study 14 cotypes of this interesting species. In ad- 

 dition, I examined several specimens from the Cornell University 

 collection and others that were given to me by Professor Gutlu-ie. 



Distribution. — Recorded as follows: 



Minnesota: St. Louis County, July 13. 1901, J. E. Guthrie (University of 

 Minnesota). 



Genus PROISOTOMA Borner 



Isoloma TuLLBERG, 1871, p. 150. 



Proisotoma Borner, 1901a, p. 134; 1903, p. 171; 1906, p. 172.— Linnaniemi, 1912, 

 p. 121. 



Genotype. — Isotoma minuta Tullberg. 



Fourth abdominal segment almost always longer than the third; 

 the two subequal, however, in a few species. Third urotergite not 

 ventrolaterally prolonged backward to any material degree. Para- 

 tergite of fourth abdominal segment distinct, not united to the tergite 

 of the genital segment. Genital and anal segments sometimes 

 ankylosed. Furcula not attaining the ventral tube in most of the 

 species. Manubrium often longer than the dentes, rarely with many 

 ventral setae, naked ventrally in a few species, but usually with one 

 subapical pair of ventral setae, rarely two or tliree pairs. Dentes 

 usually stout, with relatively few coarse transverse dorsal folds, but 

 smooth or Vvith dorsal lobes or coarse tubercles in a few species. The 

 dentes when slender and tapermg are longer than the manubrium 

 and have many fine dorsal crenulations. Mucrones commonly bi- 

 dentate or tridentate, lamellate in some of the species. Tibiotarsus 

 often with a distal subsegment. Unguiculus often with a pair of 

 inner lamellae. Tenent hairs present or absent. Postantennal organ 

 often with a notch in the middle of the anterior margin or notched on 

 both sides. Clothing of sunple setae, usually very short. Integu- 

 ment almost always smooth, but tuberculate or reticulate in a few 

 species, 



KEY TO SUBGENERA OF PROISOTOMA 



1. Dentes stout, dorsally smooth or with rounded lobes, never with 

 transverse folds. Manubrium naked ventrally. Mucrones 

 lamellate, bidentate. Tibiotarsus with a distal subsegment. 



Unguiculus with a pair of inner lamellae Ballistura (p. 39) 



Dentes dorsally with few or many transverse folds, or crenula- 

 tions, with rare exceptions. Manubrium with ventral setae, 

 usually few and subapical in position. Mucrones usually not 

 lamellate. Tibiotarsus rarely with a distal subsegment. Un- 

 guiculus rarely with a pair of inner lamellae Proisotoma (p. 43) 



