512 Stimpson on the Crustacea and Echinodermata 



joints of its feet, and perhaps aided in keeping its position 

 by the sharp dorsal setae 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 lone. The front projects abruptly, forming a hori- 

 zontal margin to the head, beneath the anterior part of 

 which the small inner antennae are concealed. The outer 

 antennae arise laterally, and behind the inner ones, which 

 they much exceed in length, being as long as half the width 

 of the head. There are no thoracic branchial appendages. 

 The thoracic feet are similar in character throughout ; they 

 gradually increase in length posteriorly, and are each pro- 

 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 papillae, one on each side, which are pro- 

 vided with short, stiff, somewhat hooked setae. The lateral 

 extremities of the abdominal segments are split by a mar- 

 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 lamellae. There are thus 

 twelve pairs of these lamellae, which are of large size, and 



