COLLEMBOLA OF THE FAMILY ISOTOMIDAE 37 



Female: Body segments relatively simple, not laterally dilated 

 (pi. 11, fig. 107). Antennal segments in relative lengths about as 

 4:9:6:10. Fourth antennal segment with long strongly curving 

 olfactory setae distally. Body segments in relative lengths as 

 9:19:21:20:18:20:24:12:6; fourth abdominal segment thus one-fifth 

 longer than the third. Clothing of numerous short curving simple 

 setae (pi. 12, fig. 115) with larger fringed setae across the posterior 

 region of segments 2 to 7, inclusive. Setae of appendages simple. 



In two females the lamellae of the mucrones showed lateral ribs 

 (pi. 12, fig. 113), not visible, however, in specimens mounted in balsam. 



Alale: Body segments 2 to 7, inclusive, laterally dilated (pi. 11, 

 fig. 108); particularly the fourth abdominal segment, of which each 

 lateral dilatation bears a stout curving horn (pi. 11, fig. 108; pi. 12, 

 fig. 116) and several clavate fringed tubercles (pi. 12, fig. 117). Seg- 

 ments 2 to 6, inclusive, have each a posterior row of large clavate 

 fringed tubercles, and bear abundant small subclavate fringed setae. 

 The fifth and sixth abdominal segments and the posterior part of the 

 fourth have numerous small capitate setae (pi. 12, fig. 118). Few 

 of the body setae are simple, except on the genital and anal segments, 

 though many simple setae occur on head, antennae, and legs. A few 

 clavate fringed setae are present on the legs and the first tw^o antennal 

 segments, and antennae and tibiotarsi bear a few tubercles. In the 

 male there is a long seta on each side of the prothorax (pi. 11, fig. 108). 

 Antennal segments in relative lengths about as 3:6:4:8. Fourth 

 antennal segment with stout lateral olfactory setae (pi. 11, fig. 119). 

 Fourth abdominal segment but slightly longer than the tliird (as 

 16:15). Anal segment small, almost concealed from above by the 

 genital segment. 



Remarks. — Guthriella muskegis exhibits secondary sexual dimor- 

 phism to an extent that is unapproached in other known species of 

 CoUembola. 



"* * * There seems no doubt that the tubercles are merely 

 modified hairs, for one finds on the same individual nearly all grada- 

 tions from the thick, stout liair with a very few short hairs at its end 

 to the much swollen tubercles with their haired areas greatly dis- 

 tended" (Gutlirie). 



"I found this species twice during the summer of 1901 in marshes 

 along the shore of Lake Vermillion, on Pine Island in St. Louis Co. 

 (Minn.). On both occasions they were on the upper ends of partially 

 submerged roots, or other decaying pieces of wood. They seem to 

 live socially, hundreds being seen together. They resemble the 

 heavier species of Achorutes in habits, being rather slow in their 

 movements. When exposed to the light, they become restless, and 

 move about uneasily seeldng for dark corners. Unless considerably 



