(in 



second pair is about as long as wide, the rami arc 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 (?) cxcurved claw. 



The caudal ati/lets are flat and broad, but narrower than in brevicauda, 

 about threc-fifth^^ 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 ma;-gins, 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 stycfius, 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, 

 ( Caecidotea, Packard). It was soon re-described by Prof. Cope, under the 

 specific name microcephahis ; 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 ^-1. aquaticus in the Crusfaces 

 rf' 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 loosed}' articulated, sides nearly parallel, 

 12 to 14 mm. by 2 to 8 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 fii'st 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 arc slightly emarginate on the 

 sides, the emarginations 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- 



