1092 Wisconsin Academy of Sciences, Arts, and Letters. 



is found on the third segment of the endopodite of the fourth 

 foot. The larger of the two terminal spines is armed on its 

 inner margin with long irregular teeth instead of the short 

 spines as is customary. (PI. LXXVII, fig. 2.) 



This feature I have found constant in specimens from the 

 northern states, but it is absent in most of those that I have 

 examined from the southern states. 



The structure of the fifth foot is like that of albidus. 



The form of the receptaculum seminis is shown in the 

 figure, Plate LXXVII, fig. G. 



The egg sacs of the female hang close to the abdomen. 



The female measures 3 to 4 mm. in length, according to 

 Schmeil. American specimens are smaller, being little over 

 half of this length. 



This species is found widely distributed in the northern 

 continents, although nowhere very abundantly. In the U. S. 

 Herrick found it in Minnesota. Later I reported it from 

 Wisconsin and Michigan. E. B. Forbes adds localities in Il- 

 linois and Massachusetts. Pearse reported it from Nebraska. 

 I have found it also in collections from Arkansas and Louisi- 

 ana, and it is probable that it is universally distributed. 



As will be seen from the literature of the subject, albidus 

 and fuscus have been confused with each other until Schmeil 

 made the clear distinction between the two species. By the 

 difference in size, the darker color of fuscus, and the different 

 habit of the egg-sacs the two are easily distinguished at a 

 glance. In albidus the egg-sacs stand out from the abdomen, 

 while in fuscus they cling close to it. In albidus there is a 

 sensory club on the twelfth antennal segment, while in fuscus 

 that segment bears a sensory hair. In albidus the hyaline 

 plate of the last antennal segment is finely serrate; in fuscus 

 it is deeply notched. In albidus the third segment of the sec- 

 ond antenna is short; in fuscus this segment is long. In albi- 

 dus the distal seta on the inner margin of the third segment of 

 the endopodite of the fourth foot is rudimentary. In fuscus 

 this seta is of the usual size, and commonly the large terminal 

 spine of this segment is armed with long irregular teeth on its 

 outer margin. In albidus the inner margins of the furcal 



