CRUSTACEA. 163 



bdella) are often found attached to the walls of the branchial 

 chamber. 



The number and variety of parasitic growths, both vegetable 

 and animal, on the carapace of this form are remarkable. 

 Balani of two species cover the back almost with a continuous 

 rugose pile, adhering to the limbs, the abdomen, the foot-jaws, 

 or each other. Coils of Serpulw and hard sandy tubes of 

 Sabellaria interlace with these and fill up the depressions, and, 

 with the former, occur on the tip of the abdomen as well as on 

 less mobile situations. Fine tufts of Sertularia pumila and 

 Crista eburnea adorn the surface of the carapace in others, or 

 the parasitic alga? thereon ; while Halichondria panicea forms 

 a thick rugged crust, from which Balani, Serpulw, Anomice, 

 zoophytes, and seaweeds emerge. Even the sockets of the 

 eyes are invaded by the sponge. Moreover young examples 

 are not unfrequently clothed with thick tufts of Obelia geni- 

 culata. It would appear that it is not always on attaining 

 full growth that moulting ceases for considerable intervals, 

 since small specimens are found as completely covered witli 

 parasitic growths. In the rock-pools the carapace often forms 

 a moving forest of seaweeds ; and in such specimens the shell 

 is frequently fragile, so that the extraneous covering may be 

 of use for protection, or else had grown with unusual rapidity, 

 even before the carapace became fully consolidated. 



One old example had the internal antennae quite fixed by a 

 hard sand-tube of Sabellaria ; and the young of the common 

 mussel are occasionally found in the cavities for the eyes. 



In the young females the genital apertures are small, and 

 the abdomen less developed ; while in the adult the latter 

 becomes hypertrophied, hollowed out on its ventral surface by 

 the bending downwards of the outer edges, and touches the 

 bases of the legs on each side. 



Hyas coarctatus, Leach ; Bell, op. cit. p. 35. 

 Common in deep water, and procured in hundreds amongst 

 the coralline ddbris in the fishing-boats ; frequent in the 

 stomachs of cod, haddock, and flounders. 



y2 



