Dr John Anderson on Phryxus paguri. 375 



teresting, and, according to its discoverer, Kathke, " 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. Bernh., 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 Bopyridae, 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 

 habitus, 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 



