Dr John Anderson on Phryxus paguri. 375 
teresting, and, according to its discoverer, Eathke, " recht 
selten parasit." As it is a new and interesting addition to 
the fauna of the Scottish seas, I shall shortly describe its 
external characters. This remarkable Bopyridian is fixed 
with its dorsal surface to P. Bernli., and from its anomalous 
position, one is apt to confound the ventral with the dorsal 
surface of the body. By means of its seven prehensile feet 
it adheres with considerable tenacity to the soft abdomen of 
the crab. In Phryxus, as in the other Bopyridse, the pro- 
portions of the female greatly exceed those of the male in- 
dividual, which is always found associated with, and leading 
a parasitic life upon, the former. Differing in size, they also 
differ in external form. 
The female always selects the left side of the crab as its 
hahituSj which, I suppose, is owing to this side of the crab 
being always in relation to the widest part of its appro- 
priated dwelling. It is about half an inch in length and a 
quarter of an inch in breadth ; all my specimens were of a 
pure white colour. The body of the animal, with the excep- 
tion of the caudal appendage, is nearly of the same breadth 
throughout its whole extent ; its anterior margin is rounded. 
As already stated, the dorsal surface is applied to the 
abdomen of the crab, and is flat, but slightly concave in the 
centre, and is divided into seven segments, each segment 
bearing a pair of prehensile feet. The ventral or upper- 
most surface is in relation to the shell in which the crab 
lives, and, like the dorsal, is distinctly segmented, but is 
hidden from view by six leaf-like membranes, which form 
the breeding cavity for the ova. 
The head of the animal cannot be detected on the ventral 
surface until the bladder-like pouches which overlap it are 
removed. This portion of the head consists of a large under 
lip, behind and over which are placed two valve-like bodies ; 
these bodies, in reality, are the altered pouches of the head 
segment. When viewed from the dorsal aspect, the head 
has a quadrangular appearance, bearing upon the centre of 
its anterior margin a small rounded process. The first pair 
of antennae are small, and consist each of three joints, the 
terminal joint bearing a few bristles. The second pair are 
VOL. II. 3 c 
