( 13 ) 
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. (See 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 stylets 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 incubatory 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 
species is found quite frequently in deep wells of central Illinois, in com- 
pany with, but much more abundant than, Crangonyx 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). 
Eubranchipus serratus, Forbes. This species seems to replace the 
E. vernalis , Verrill , 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 segments , 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. The frontal appendages of the male 
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 
