THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[FOURTH SERIES.] 



" per litora spargite museum, 



Naiades, et circiun vitreos considite fontes: 

 Pollicc \-irgineo teneros h'lc carpite floras : 

 Ploribus et pictum, divae, replete canistrum. 

 At vos, o NjTnphae Craterides, ite sub undas; 

 Ite, recurvato variata eorallia truneo 

 Vellite muscosis e rupibus, et mihi conchas 

 Perte, Dese pelagi, et pineui conchylia succo." 



If. Parthenii OiannettasWEd. 1. 



No. 61. JANUARY 1873. 



I. — Transformation of an entire Shell into Chitinous Struc- 

 ture hy the Polype Hydractinia, icith short Descriptions of 

 the Polypidoms of five other Species. By H. J. CARTER, 

 F.R.S. &c. 



[Plate I.] 



All who are acquainted with the Spongiadse know that there 

 are certain species which enter the substance of shells and 

 there grow to such an extent that finally the whole shell which 

 they inhabit may become absorbed or destroyed, and the sponge 

 itself, thus left alone, become unattached ; after which it may 

 still go on increasing in size until, drifted about by the currents 

 in the sea, it may at last in some storm be thrown ashore 

 upon the beach. Cliona celata, which attacks the oyster-shell, 

 is one of these, and after having absorbed the whole valve 

 grows into a shapeless mass, which is brought up by the trawl- 

 or dredge-net, or cast ashore, as before stated, in which con- 

 dition it has been called "Baphyrits Grifiithsii^^ by Dr. Bower- 

 bank. Halichondria suberea, Jolmst., is a species which 

 attacks univalve shells — but often retains more or less of the 

 outward form of the shell, and almost always that of the in- 

 ternal cavity ; for a hermit crab [Pagurus) generally inhabits 

 the latter, and so prevents the sponge from encroaching in 

 this direction. Hence, if the outward form of the shell is lost, 

 the internal one is, for the most part, so perfectly preserved 

 that there is no difficulty whatever in concluding that it was 

 Ann. <& Mag. N. Hist. Ser. 4. Vol. xi. 1 



