a new Group of Parasitic Crustacea. 47 



often seen behind the orifice of the brood-chamber makes me 

 think an aperture in this place not improbable. 



I looked for males of Lernceodiscus the more zealously as 

 Rathke observed in the brood-chamber of Peltogaster Paguri a 

 small Crustacean, his Liriope pijgmaa, but hitherto without any 

 result. In the fluid obtained from the above-mentioned large 

 glands I have, on the contrary, seen motile particles, the exact 

 form of which my microscope is not capable of showing. From 

 their mode of moving, I scarcely hesitate to regard the fluid as 

 semen. 



Sacculina purpurea (PI. II. figs. 4 & 5), the parasite of our 

 small Hermit Crab, appears to be no less plentiful than the 

 Lernaodiscus. After my attention had once been directed to it, 

 I could obtain from the shells collected during a single ebb-tide 

 thirty or more Paguri with the parasite attached to them. The 

 parasite adheres, in the form of a thick, slightly bowed cushion, 

 of a purple-red colour, which was observed more than 6 millims. 

 in length and half that thickness, to the base of the soft abdomen, 

 and on its left and more convex side; its somewhat thicker pos- 

 terior extremity, with the orifice of the brood- chamber, is turned 

 towards the head of its host, and therefore towards the mouth 

 of the shell. The point of adhesion is on the concave side of 

 the cushion, rather nearer to the posterior extremity ; from 

 above, the extremities appear to be rounded-off in a spherical 

 form. 



The parasite is just as much obliquely twisted as its host. If 

 we regard the concave surface, by which the animal adheres, as 

 the lower one, and determine the posterior extremity by the 

 presence of the aperture of the brood-chamber, then, of the two 

 sides, which are distinguished beneath by the intestine and 

 ovary, and on the back by a shallow furrow, the left is most 

 developed posteriorly, and the right anteriorly. In front the 

 difference is inconsiderable ; but posteriorly it is so great, that 

 the orifice of the brood-chamber is completely displaced towards 

 the right angle of the posterior margin. This orifice forms a 

 small longitudinal fissure, and exhibits the same currents of 

 water as in Lernceodiscus, On the left side, the posterior margin 

 runs out into a more or less distinct acute angle. The intestine 

 and the ovary which lies over it form a rather narrow stripe, 

 diminishing anteriorly and posteriorly, which extends from the 

 point of attachment forward nearly to the anterior margin, and 

 backward to the orifice of the brood-chamber. The whole re- 

 mainder of the cushion is brood-chamber. The approaching 

 maturity of the eggs is betrayed by a paler and more translucent 

 coloration. 



The concentrically grooved shield at the point of attachment 



