second pair is about as long as wide, the rami are as long as the 
pedicel and sub-equal. The second joint of the outer ramus is ellipti- 
cal and thrice as long as the first. The inner ramus is nearly half 
as wide as long, the basal processes obtuse and low, the outer one 
being almost obsolete. The outer terminal angle is prolonged into an 
incurved process, the inner provided with a movable (?) excurved claw. 
The caudal stylets are flat and broad, but narrower than in brevicauda, 
about three-fifths as long as the abdomen. The width of the pedicel is two- 
thirds its length. The outer ramus is nearly five-sixths the inner and equal 
to pedicel. Both rami are narrow-ovate, and very obtuse, the inner about 
four times as long as wide and nearly straight on the outer margin. Both 
pedicel and rami are spiny on their margins, and the latter are tipped with 
a few long hairs. 
Abundant in the hill-country of southern Illinois, under stones in small 
streams. 
While these two species of Asellus were found in considerable numbers 
on the first day of my trip, I have never seen a specimen of either in the 
central or northern part of the state, although I have carefully searched the 
most varied situations. 
Asellus stygius, Packard. This species has been peculiarly unfor- 
tunate. Described originally from an injured specimen, its structure and 
relations were misunderstood and it was made the type of a new genus, 
( Caeddotea , Packard). It was soon re-described by Prof. Cope, under the 
specific name microcephalus ; and these imperfect descriptions have since 
been supplemented by several fragmentary notices in various papers by 
Packard and Smith. 
With a view to giving a more coherent account of it, 1 have examined 
many specimens of both sexes and various ages, and have prepared the fol- 
lowing description : A detailed comparison of this species with undoubted 
Asellus — especially with the admirable plates of A. aquaticus in the Crustaces 
d J eau douce de Norvege , has failed to reveal any structural peculiarities 
which could possibly serve as the characters of a distinct genus, and I have 
therefore united it to Asellus. 
Colorless, blind, narrow, very loosely articulated, sides nearly parallel, 
12 to 14 mm. by 2 to 3 mm. 
The head is a little narrower and longer than the first thoracic segment, 
narrower in front than behind, with the front margin concave, the front 
angles rounded, the hind margin nearly straight. It is a little constricted 
behind the mandibles. The first thoracic segment is narrowed a little to the 
front so as to show the epimera, the sixth and seventh are also much narrower 
before than behind, and longer than the others. The front angles of the 
second and third segments are obliquely truncate, the hind angles broadly 
rounded. All the segments behind the first are slightly emarginate on the 
sides, the einarginations being carried gradually backward to the posterior 
angles. The anterior margins of the segments change gradually from con- 
cave to convex, and the posterior margins from sinuate to deeply concave. 
The head and all the segments are slightly pubescent above and bor- 
