216 Mr Cooke, On Parasitic Mollusca. [May 18, 



small Buccinum. As the coral (Meandrina) to which it attaches 

 itself grows, it develops at the mouth a long calcareous tube, the 

 aperture of which keeps pace with the growth of the coral, 

 and prevents the mollusc from being entombed. The animal 

 lives at the free end of the tube, and is thus continually shifting 

 its position, while the space it abandons becomes completely 

 closed by calcareous matter. Certain species of Ovula inhabit 

 Gorgoniae, assuming the colour, yellow or red, of their host, and, 

 in certain cases, developing for prehensile purposes a pointed 

 extension of the two extremities of the shell. Pedicularia in- 

 habits the common Melithaea rubra of the Mediterranean, and 

 another species has been noticed by Graeffe 1 on M. ochracea in 



Fi J l 



On Echinodermata. (a) Grinoidea. Stilina comatuhcola lives 



on Comatula mediterranea, fixed to the outer skin, which it pene- 

 trates by a very long proboscis ; the shell is quite transparent 2 . 

 A curious case of a fossil parasite has been noticed by Roberts 3 . 

 A Calytraea-sh&iped shell named Platyceras always occurred on 

 the ventral side of a crinoid, encompassed by the arms. For 

 some time this was thought to afford conclusive proof of the 

 rapacity and carnivorous habits of the echinoderm, which had 

 died in the act of seizing its prey. Subsequent investigations, 

 however, showed that in all the cases noticed (about 150) the 

 Platyceras covered the anal opening of the crinoid in such a way 

 that the mouth of the mollusc must have been directly over the 

 orifice of the anus, (b) Asteroidea. The comparatively soft tex- 

 ture of the skin of the starfishes renders them a favourite home 

 of various parasites. The brothers Sarasin noticed 4 a species of 

 Stilifer encysted on the rays of Linckia multiformis. Each shell 

 was enveloped up to the apex, which just projected from a 

 hole at the top of the cyst. The proboscis was long, and at its 

 base was a kind of false mantle, which appeared to possess a 

 pumping action. On the under side of the rays of the same 

 starfish occurred a capuliform mollusc (Thyca ectoconcha), fur- 

 nished with a muscular plate, whose cuticular surface was indented 

 in such a way as to grip the skin of the Linckia. This plate 

 was furnished with a hole, through which the pharynx pro- 

 jected into the texture of the starfish, acting as a proboscis and 

 apparently furnished with a kind of pumping or sucking action. 

 Adams and Reeve 5 describe Pileopsis astericola as living ' on the 

 tubercle of a starfish,' and Stilifer astericola, from the coast of 



1 Described as a Cypraea, but no doubt an Ovula or Pedicularia: C. B. Bakt. 

 Par. v. 543. 



2 Von Graff, Z. Wiss. Zool. xxv. 124. 



3 Proc. Avier. Phil. Soc. xxv. 231. 



4 Ergeb. naturw. Forsch. Ceylon, abstr. in J. R. 31. S. (2) vi. 412. 



5 Voyage of the Samarang, Moll. p. 69, PI. xi. f. 1 ; p. 47, PI. xvn. f. 5. 



