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, hut 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. Eorbes 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 fureal 
