68 BULLETIN 168, UNITED STATES NATIONAL MUSEUM 



anterodorsal region of the genital segment, close to the suture between 

 the fourth and fifth urotergites; (2) a pair on the anterodorsal region 

 of the anal segment, close to the obsolete suture between the genital 

 and anal segments. 



Denis (1926) says that in males longer than 1.1 mm the antennae 

 are longer in relation to the head than in females. 



In specimens from Massachusetts some of the stiff outstanding 

 setae of body, legs, and antennae are thickened and spinelike, as 

 in plate 14, figure 149 — a condition that I have not yet found in 

 Arctic material. 



Through the courtesy of Dr. A. S. Packard I once examined 18 

 cotypes of this species from Polaris Bay, latitude 81°20' to 81°50' N. 



A. besselsi is a littoral species, limited to the seashore or its vicinity, 

 and commonly found between tide marks, where it occurs under 

 stones, seaweed, or driftwood, or burrowing in the sand, or exposed on 

 the shore. It is an agile species and a vigorous jumper, as mentioned 

 by Davenport (1903) in his interesting account of the distribution and 

 movements of littoral Collembola. 



Cotypes.— V.S.'NM. no. 43002. 



Distribution. — There are records of the occurrence of this species 

 in Jan Mayen Island, Spitsbergen, Nova Zembla, Russia (Kola 

 Peninsula), Finland, Norway, France, Scotland, England, and Tierra 

 del Fuego. The species ranges from northern Greenland almost to 

 the Antarctic Circle, and probably owes its exceptional distribution 

 to marine currents. 



Greenland: Polaris Bay, July 5, Dr. Bessels (U.S. National Museum). Umanak, 

 June 28, July 26, M. C. Tanquary (American Museum of Natural History; 

 University of Illinois). 



Massachusetts: Neponset, May 4, October 7, 10. 



New York: Cold Spring Harbor, Long Island, July, C. B. Davenport. 



California: Laguna Beach, G. A. Bacon. 



Genus AGRENIA Horner 



Isotoma TuLLBERG, 1870, p. 34 (part). 



Agrenia Borner, 1906, p. 171. — Linnaniemi, 1912, p. 173. 



Genotype. — Isotoma bidenticulata Tullberg. 



Unguis with a basal membrane connecting the strong lateral teeth. 

 Dentes twice as long as manubrium, stout, slightly narrowing distally, 

 not crenulate dorsally, but with coarse rounded tubercles, with a 

 very long subapical seta. Furcula long, attaining the ventral tube. 

 Manubrium with many ventral setae. Mucrones lamellate. Corpus 

 of tenaculum with very many setae. Third and fourth abdominal 

 segments subequal in length, or third a little longer. Genital and 

 anal segments ankylosed. Tibiotarsus without a distal subsegment. 

 Unguiculus with a pair of inner lamellae. Tenent hairs absent. 

 Clothing of short simple setae. 



