behind, the tip of the second pair reaching as far as the base of the propodus 

 of the seventh. The abdominal sexual plates of the male are in two pairs, 

 as usual. (8eo plate). The corresponding plates of the female are but one 

 pair, rather narrowly ovate, ciliated at tip and on posterior two-thirds of 

 outer margin, with a few short spines at the base of the inner edge. The 

 external ramus of the next pair — serving as a gill-cover — bears a terminal 

 fringe of plumose hairs and a few short spines at base on outer margin. The 

 inner ramus — first gill — is oblong, two-thirds the length and breadth of the 

 outer. Both the pedicel and rami of the caudal sti/lets are slender and 

 cylindrical, the former about as long as the last two joints of the last pair 

 of legs, the latter tipped each with a cluster of bristles, the inner about 

 two-thirds as long as the pedicel, the outer varying from one-quarter to two- 

 thirds the inner. The length of the rami varies greatly with age and sex. 

 In many old males the inner is very long and the outer minute. There are 

 four pairs of incubator// lamellae in the female, each pair overlapping by 

 their rounded inner ends, except the first, which are shorter and have the 

 anterior internal angles emarginate. 



The description has been given above in greater detail than would 

 otherwise have been necessary, in order to settle the question of genus. The 

 specic.>- is found quite frequently iu deep wells of central Illinois, in com- 

 panv with, but much more abundant than, Crangom/x mucronatus. 



After a long period of heavy rains during the last summer had greatly 

 swelled the subterranean streams which these species inhabit, they appeared 

 at the surface in springs, and even at the mouths of tile drains, in such 

 numbers that a hundred could be taken in an hour. A few females were 

 observed with eggs at this time. (July). 



Euhranchipus sen-atus, Forbes. This species seems to replace the 

 E. vernalis, Vrrrill, of the Eastern States, to which it is closely allied. An 

 important character, constant in the large number of both sexes which I 

 have examined, is found in the abdominal ser/ments^ which are narrowed in 

 front, with rounded anterior angles, while the posterior angles are produced 

 backward, giving a decidedly serrate appearance to the abdominal margin. 

 The last two abdominal segments are closely united and broader than the 

 preceding. 



Tne antennae extend a little beyond the eyes, and terminate in a cluster 

 of about five slender olfactory clubs. Tho frontal appendnr/es oi the mdle 

 are considerably longer than the claspers, to the front inner base of which 

 they are attached, the line of attachment being parallel to the length of the 

 basal joint. Their form is irregularly oval, the inner edge being regularly 

 convex on its distal three-fourths and the outer sinuate — convex on basal 

 two-thirds, and .slightly concave on terminal third. Both margins are 

 pectinate, except near base, with thick blunt teeth, which are longest on the 

 basal half of the outer margin, where they are as long as the undivided part 

 of the appendage is wide. At the middle of this margin the teeth become sud- 

 denly shorter. On the inner margin they are longest near the middle, regularly 

 lessening towards each end. The under (posterior] surface of the appendage, 

 as well as the teeth, is set with short spines, each springing from an inflated 



