484 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 50. 



35 to 39; the erect capitate setae characteristic of typical jyackardi 

 are absent, though some of the setae on the posterior part of the abdo- 

 men may be obscurely capitate. In other respects the variety agrees 

 with the typical form. 



I have found this variety under the loose bark of pine, red maple, 

 and oak trees, especially at the base of the roots; and it occurs 

 sometimes on snow. In Massachusetts it has at least three broods, 

 which mature at intervals of six or seven weeks. 



Dentatus is a seasonal variety of iiackardi. I have raised the latter 

 from eggs of the former, which hatched May 20 (Massachusetts). 



I agree with Linnaniemi ('12, p. 32) that his A. lap2)onicus of 

 Finland and Sweden is probably this variety dentatus. The distal 

 tibiotarsal hairs are often feebly clavate in dentatus and apparently 

 strongly clavate in lapponicus. The name dentatus (March, 1902) 

 antedates lapponicus C'Mitgeteilt am 5. April, 1902"). 



Maine. — Orono, March 10, 15, May 1, 3, F. L. Harvey. 



Massachusetts. — ArUngton, April 10, 13, 23, 30, May 23, Sep- 

 tember 10. 



New York. — Ithaca, April 12, A. D. MacGilUvray. , Ghent, April 

 13, E. C. Powell (N. Y. State Coll.). 



Ohio. — Salem, March 18, A. D. MacGilUvray. 



ACHORUTES SOCIALIS Uzel. 

 Plate 7, fig. 1; plate 10, figs. 42-4G; plate 11, figs. 47-50. 



Podura nivicola Fitch, 1847. 



Achorutes sodalis Uzel, 1890.— Schott, 1894o, 18966, 1902.— Schaffer, 1896.— 

 Carl, 1899, 1901.— Reuter, 1900.— Absolon, 19016.— Lie-Pettersen, 

 1901. — Krausbauer, 1902. — Guthrie, 1903. — Wahlgren, 19066. — (Axel- 

 son) Linnaniemi, 1907. 



SchoLurus nivicola MacGillivray, 18936. — Dalla Torre, 1895. 



Achorutes diva'siceps Lintner, 1896. 



Achorutes spinifer Schaffer, 1896. 



Achorutes nivicola Folsom, 1902a. — Axelson, 1904. — Lie-Pettersen, 1907. 



Ilypogastrura socialis Linnaniemi, 1912. 



Dark indigo blue throughout. Eyes (fig. 42) eight on each side. 

 Postantennal organs (fig. 43) with four peripheral tubercles. Anten- 

 nae about as long as the head, with segments as 7:9:10:15; basal 

 segment subglobose, second and third subcylindrical, fourth rounded 

 conical. Olfactory hairs of fourth antennal segment (fig. 44) six to 

 ten — four to eight outer and two inner. Sense-organ of third antennal 

 segment (fig. 45) with two oblong-clavate curving processes. Body 

 elongate, abdomen subfusiform, last segment subcylindrical. Unguis 

 (fig. 46) slightly curving, with inner margin unidentate about one- 

 third from the apex. Unguiculus extending about half as far as 

 unguis, basally subovate, apicaUy acicular. One long tenent hair 

 with a minute knob. Distal tibiotarsal hairs apically bent and often 

 feebly Imobbed. Dentes (fig. 47) stout, subcylindrical, apicaUy 



