188 CORRESPONDENCE. 



Mr. Waller endorses Dr. Bowerbank's view in reducing all the 

 burrowing species of sponges enumerated by Mr. Hancock to the one 

 CUona celata. This statement is quite sufficient to convince me that 

 Mr. W. has never seen another not uncommon species with similar 

 habits to C. celata, namely, Clione Nortfiumhrica, Hancock. This 

 species is as distinct as any two species of a genus in all our British 

 sponges, and I have no doubt but that Dr. Bowerbank will establish 

 this as a species in his forthcoming volume on the additional species 

 to his former volume on the British Spongiadae.* There is, as I have 

 stated in my paper, a very great similarity in the erosive workings of 

 both annelids and sponges. The same may be said of the action of an 

 acid on shell or limestone ; and although I cannot prove by any test 

 that these creatures use an acid for eroding their burrows, I feel 

 convinced that such is the case. Take, for instance, the habit of 

 Halichondria suheria and H. fims ; these species frequently invest 

 the shell on which they attach themselves, and when this is the case, 

 the shell becomes entirely dissolved, leaving its form entire in the 

 inside of the sponge. The mere finding of an oyster-shell perforated 

 full of minute holes, as stated by Mr. Waller, is not sufficient evidence, 

 unsuj)ported by facts, to convince anyone knowing anything of this 

 subject. 



Still pursuing this subject, I have added since I published my 

 paper last year another fact in relation to the biuTowing annelids. 



In tracing the burrow of an annelid in an old shell of Buccinum 

 undatiim cast ashore at Exmouth, the burrow, I may say, was quite 

 recent ; it follows the direction of the whorls of the shell, keeping 

 near the sutures ; the hole is more or less irregularly excavated in a 

 lateral direction, a transverse section of the burrow shows it to be 

 nearly quadrate, with the above irregularity absent ; but the most 

 remarkable thing to me, and so far as I know it is new in the history 

 of these burrowing annelids, is this, this burrow is regularly divided 

 by transverse septae. The diameter of the burrow is y^^th of an inch, 

 and the septse vary from the ^Vth to the t" 5*^ of an inch apart. The 

 septse are made up of very thickly-woven threads of what appear to 

 be chitine. The object in building up these barriers across the 

 burrow appears to me to be to protect the creature when at work, or 

 to prevent the water diluting the erosive agent too much. Some 

 water would naturally be left in the hole after the barrier was con- 

 structed, and this, no doubt, is quite sufficient for the creature's wants. 

 But in this mode of working, the waste of material in building up 

 these numbers of scptse must be immense on a small animal like this. 



Unfortunately the annelid had escaped by a hole in the surface of 

 the shell before I found it, I am therefore quite ignorant of the 

 species which makes this remarkable burrow. 



I am. Sir, yours obediently, 



Edward Parpitt. 



* See also remarks on this, 'Ann. Nat. Hist.,' 1870, pp. 80, 81. 



