Mr. J. S. Bowerbank on the Siliceous Bodies of the Chalk. 253 



body to which they are attached be a sponge. But where, says 

 the author, are such specimens to be found ? I answer, in my own 

 collection, and I will show him dozens such if he will favour me with 

 a visit to see them ; and I assure him that that which he considers 

 as so very improbable is in truth the natural habit of the Spon- 

 giadse, which attach themselves to both living and dead shells, 

 and in that situation they develope themselves to their full ex- 

 tent, freely rolling about as the tidal or other currents impel 

 them. I have a specimen of Area with a sponge firmly based 

 upon one valve and loosely embracing the other, and which is 

 many times the bulk of the shell, and the animal still remaining 

 within the shell. Area, Pecten, Hinnites, Ostrea, and numerous 

 other bivalves, are frequently to be seen thus encumbered with 

 large sponges ; and I have also a large keratose sponge from Port 

 Lincoln, Australia, which has more small univalve shells entangled 

 in its meshes than could be counted correctly in a long summer^s 

 day ; but we need not go to exotic specimens for such proofs, for 

 if the author had only taken the precaution to have consulted 

 Dr. Johnston^s excellent ' History of British Sponges,^ he would 

 have found it quite unnecessary to have gone further to have sa- 

 tisfied himself of the fallacy of his own imaginations regarding 

 the habits of the Spongiadse, and I beg to refer him to plates 8, 

 5, 12, 14 and 15 of that work as pictorial proofs to the contrary 

 of his assertion ; and it is well known to every man who has paid 

 the slightest attention to marine natural history, that Halichondria 

 suherea described by Dr. Johnston, p. 139. fig. 5 and 6. pi. 12, 

 is rarely met with, excepting partially or wholly enveloping uni- 

 valve shells, and that these shells are usually inhabited by a Pa- 

 gurus. I have brought up a dozen or more of such specimens at 

 each haul of the dredge in Weymouth Bay and in the neighbour- 

 hood of Tenby, and I have many such in my possession at the 

 present moment. It is as much the habit of the animal to be 

 parasitic upon shells, as it is for Dromia lator and other species 

 of the genus, during its life, to carry a living ambush of sponge 

 upon its back, to secure which in its proper situation nature has 

 stinted the growth of the two hinder pairs of legs, and directed 

 them over the back of the animal to hook into and hold firmly 

 the mass of sponge under which it lives and moves. 



There is also another crab, which 1 believe belongs to the genus 

 Pericera, which is in the constant habit of cherishing the growth 

 of long fistulose sponges on the front spines of its shell, and these 

 sponges often attain three or four times the length of the crab. 

 I have in my possession at the present moment five specimens of 

 the latter and ten of the former, bearing each his sponge ; and in 

 one case the mass of sponge is as big as my two fists placed 

 together, and in several of the smaller ones the sponge is so big 



