a new Parasitic Isopod Crustacean. 89 



reach to the extremity of the penultimate segment. The feet 

 can not only be raised and depressed, but also extended laterally. 

 The last segment of the abdomen is truncated at the apex above, 

 and has on its lower surface a V-shaped notch reaching to its 

 middle. On the veutral surface of the first and second abdomi- 

 nal segments, and less developed on that of the third, there is 

 on each side a very prominent contractile fold of skin ; its 

 strongly undulated margin contains a vessel-like cavity, which 

 is continued into the margin of the corresponding foot. 



At the base of the first abdominal segment its dorsal surface 

 bears a hernioid diverticulum, of about 05 mill, in length and 

 the same in height ; in this is the heart, which pulsates rather 

 sluggishly. 



Although in the structure of the female the cseca at the com- 

 mencement of the alimentary canal, the two hepatic tubes, and 

 the heart situated at the base of the abdomen scarcely remind 

 one of Bopyrus, the affinity to that Isopod shows itself unmis- 

 takeably in the males (PI. II. fig. 9), which, as in Bopyrus, are 

 the almost constant companions of the female, but are much more 

 diminutive, and therefore may easily be overlooked amongst the 

 immense masses of the eggs. In general there is only one of 

 them ; in a single instance I saw two walking about upon the 

 body of the same female. 



The male is about 0'8 millim. in length, or scarcely 3-4 

 times the length of the newly hatched young; in the middle of 

 the thorax the breadth attains nearly 3 of the length ; and from 

 this point the body diminishes slightly in front, and greatly be- 

 hind. The thorax is distinctly separated into seven, and the 

 abdomen into six segments; but the boundary between the head 

 and the first thoracic segment is indicated only by a deep lateral 

 constriction. The head is trapezoid in form, with rounded 

 angles ; its height is about equal to the shorter of the parallel 

 sides, and to the half of the longer posterior one. It bears a 

 pair of short, inarticulate, flat, quadrangular antennae; by the 

 inner side they spring from the lower surface of the head, the 

 anterior side coincides with the frontal margin, the posterior is 

 nearly parallel to this, and the outer side runs obliquely back- 

 wards and outwards. On the anterior obtuse angle, there stands 

 a group of short bristles, curved inwards. The eyes are often 

 wanting ; when present, they are moved backwards from the 

 head nearly to the posterior margin of the first thoracic segment, 

 which coalesces with it. The triangular rostrum originates at the 

 hinder limit of the head ; its apex lies between the origin of the 

 antennse. 



The six anterior thoracic segments bear near the margins feet 

 reduced to nearly sessile, inarticulate, roundish lumps, with 



