512 Stimpson on the Crustacea and Echinodermata 
joints of its feet, and perhaps aided in keeping its position 
by the sharp dorsal sete of the abdomen. As might be ex- 
pected from this external parasitism, the shape of the body is 
symmetrical, being never distorted, as is almost always the 
case in those forms which live in the usual position—in the 
confined space under the thoracic shield of the shrimp or 
cray-fish. 
In our species the thorax is somewhat cordate in shape, 
broadest behind, the short abdomen being set in the con- 
cavity. The thoracic segments are well separated and pro- 
vided with distinct tumid epimera; the external envelope 
-is soft, being even less hard and crustaceous than in Argeia. 
The head is somewhat broader than long, strongly tumid, 
and in the character of its appendages resembles somewhat 
that of Jone. The front projects abruptly, forming a hori- 
zontal margin to the head, beneath the anterior part of 
which the small inner antenne are concealed. The outer 
antennz arise laterally, and behind the inner ones, which 
they much exceed in length, being as long as half the width 
ofthe head. There are no thoracic branchial appendages- 
The thoracic feet are similar in character throughout; they 
gradually increase in length posteriorly, and are each po 
vided with a small hand, the hooked finger of which is of 
moderate length, more than reaching the projecting inferior 
angle of the antepenultimate article. ; 
The abdomen is triangular, and consists of six deeply 
separated segments, the terminal one being very minute. 
The basal segment is much the largest, and bears upon its 
dorsal surface two papilla, one on each side, which are pro" 
vided with short, stiff, somewhat hooked sete. The lateral 
extremities of the abdominal segments are split by a pagi 
ginal furrow into superior and inferior rami; the latter being 
simply conical with two or three circular wrinkles; and the 
former (superior) each surmounted by a cylindrical pedicle 
which bears two large cultriform lamelle. There are thus 
and 
twelve pairs of these lamelle, which are of large size ® 
