( 8 ) 
appendage, usually about as long as the first three abdominal segments, and 
as large as the last joint of the pedicel of the lower antenna. It presents a 
very slight double curve, is obliquely rounded at the end and tipped by a 
cluster of short hairs. In some cases this appendage is half as long as the 
body. 
The female differs in the following particulars. The upper antennae 
are only about half the length of the body, the flagellum not more than 
three times as long as the pedicel, and the secondary flagellum is usually a 
little shorter. The propodus of the first pair of feet is similar in outline, but 
the palmar margin and dactyl are shorter and the posterior margin longer. 
The second pair are extremely like the second of the male, but are decidedly 
smaller than the first. The telson affords a difference so remarkable that 
the two sexes, at first sight, would hardly be referred to the same genus. 
In the female this is very similar to the telson of C. gracilis , Sm. It is 
flattened and slightly emarginate, a little longer than broad, extending to 
the tips of the second pair of anal legs, and bears two terminal clusters of 
spines of four or five each. 
This species was first discovered by me in a well at Normal, 111., during 
the summer of 1875. It was subsequently found by Mr. Harry Harman in 
great numbers in springs, and even at the mouths of drains, after a long pe- 
riod of heavy rains. With the advent of dry weather it entirely disappeared 
from these, but still occurs sparingly in wells. 
Asellus brevicauda , Forbes. Length without caudal stylets, 10 mm. 
to 15 mm.; width, 3 mm. to 5 mm. Color as in A communis. Head a little 
longer than first thoracic segment and about two-thirds as wide : anterior 
margin distinctly concave in middle and retreating each side, anterior angles 
distinct, sides straight, nearly parallel on anterior three-fourths. 
The posterior fourth is produced on each side into a prominent lateral 
lobe bearing several stout spines. The distance to which this lobe projects 
equals half the length of the lateral margin of the head in front of it. The 
eyes are rather small but prominent, and are situated just within the middle 
of the straight portion of the lateral margin. The re-entering angle at the 
side of the head is a little less than a right angle, but its apex is rounded. 
The thoracic segments are sub- equal in length, of the usual shape, but be- 
coming very concave behind. The concavity of the last segment amounts 
to more than half the length of the segment. The anterior angles of the 
first segment are deeply emarginate, the notch being nearly filled by the 
epimeron ; but there are no other lateral emarginations in any of the seg- 
ments, nor are any other epimera visible from above. In some young speci- 
mens the lateral margins of the two or three posterior thoracic segments are 
slightly sinuate. The hind angles are all rounded, and the free margins are 
all beset with long bristles, longest on the lateral margins and especially at 
the angles. 
A short first abdominal segment is visible in the concavity of the last 
thoracic. The last abdominal is wider than long, with a broad rounded 
projection occupying the median half or two-thirds of the posterior margin, 
reaching half way or more to tips of pedicels of caudal stylets. The pos- 
