154? Natural Histo)^ of Molluscans Animals, 



Crowds of the inferior animals certainly feed on the Mollusca'^ 

 but as there is little interest in the detail, a very few examples 

 will here suffice. Two small leeches (//irudo bioculata and 

 complanata) often wage successful war against the fresh-water 

 snails so abundant in our ditches ; and another species [H. 

 hyalina), not so cruel in disposition, draws its nourishment 

 from the sanies which flows from the Planorbis carinatus. 

 Its calcareous envelope is no protection to the muscle against 

 the wiles of the Nymphon grossipes ; thousands of littoral 

 shells are devoured by the sea anemones ( Actmise) ; and the 

 common star-fish knows so well how to force the oyster from 

 his close retreat *, and destroys such numbers of them, that 

 every dredger who observes one of their enemies, and does not 

 tread on and kill it, or throw it upon the shore, is liable ta 

 some penalty. 



As ultimately connected with our subject, I must now inform 

 you that to some animals among the inferior tribes, shells afford 

 a house and a place of refuge, as necessary to them as either 

 air or food* The turbinated univalves become, after the death 

 of their proper owners, the habitations of the soldier or hermit 

 crabs (Pagurus Leach\ whose naked and slender abdomens, 

 covered merely with a skin of a delicate texture, would, with- 

 out this foreign covering, be crushed to pieces in the strife of 

 waves and rocks to which they are exposed, or devoured by 

 the enemies which surround them. A singular species of 

 soft worm, or Siphunculus, discovered by Mr. Montagu, inha- 

 bits old and worn specimens of the ^Strombus pes Pelecani 

 Lin,, whose aperture it closes up with agglutinated sand, leav- 

 ing only a small round hole, within which it lives in security ; 

 and another species not yet described, though common on the 

 coasts of Scotland, takes possession of the common tooth-shell 

 (Dentalium entalis), and secures the aperture in the same man- 

 ner. The beautiful and delicate Paper Nautilus, with whose 

 interesting history you must be, at least, partially acquainted, 

 is not navigated over the surface of its native ocean by its own 

 architect, but by a species or Ocythoe, or cuttle-fish, its para- 

 sitic inhabitant. This surprising fact was long disputed 

 amongst naturalists ; but the specimens brought to England 

 by the gentlemen of the unfortunate Congo expedition, have 

 enabled Dr. Leach and others to give it very great probabi- 



* " The prickly star creeps on with fell deceit. 

 To force the oyster from his close retreat. 

 When gaping lids their widen'd void display, 

 The watchful star thrusts in a pointed ray. 

 Of all its treasures spoils the rifled case, 

 And empty shells the sandy hillocks grace.'* Jones, 



