ISOPODS OF NORTH AMERICA. ' 543 



The following description of the female is given by Stimpson: 



This curious form of parasitic anisopods was found attached to and lying between 

 the abdominal feet of the common Gebia, adhering by the sharp hook-shaped termi- 

 nal joints of its feet, and perhaps aided in keeping its position by the sharp dorsal 

 setse of the abdomen. As might be expected 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 crayfish. 



In our species the thorax is somewhat cordate in shape, broadest behind, the 

 short abdomen being set in the concavity. The thoracic segments are well separated 

 and provided with distinct tumid epimera; the external envelope is soft, being even 

 less hard and cru^taceous 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 horizontal 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 provided 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 provided with 

 short, stiff, somewhat hooked setae. The lateral extremities of the abdominal seg- 

 ments are split by a marginal 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 cultriforni lamella?. 

 There are thus twelve pairs of these lamellae, which are of large size, and being 

 crowded, project in different directions, nearly concealing the posterior half of the 

 animal. Each is about one-fifth as broad as long, compressed on the inner and 

 thickened along the outer or convex edge. Only females of this species have as yet 



been found, The dimensions of one specimen are: 



Inch. 



Length of body 0. 58 



Length of abdomen 12 



Length of superior abdominal appendages 24 



Breadth of thorax .. 45 



Several examples of this singular crustacean have been found on Gebise from Puget 

 Sound and Tomales Bay. rt 



Lockington says: "The males do not live attached to the Gebia, but 

 are free to rove." His description of the male is as follows: 



Head semi-circular anteriorly, closely united to the succeeding segment. Third 

 and fourth thoracic segments widest. Body oblong, boat-shaped, tapering slowly 

 from the fourth to the seventh thoracic segment. 



Outer antennae 4-jointed; inner very small, reaching about to the middle of the 

 second segment of the outer. Eyes too small to be distinguished by a Coddington 

 lens. First abdominal segment a little narrower than last thoracic, but flat; succeed- 

 ing segments tapering rapidly to the sixth or telson, which is pointed at the end and 

 is provided on each side with a small lamella, giving the whole telson somewhat the 

 appearance of a spearhead. 



a Bost. Journ. Nat. Hist., 1857, pp. 511-513. 



