NOTE ON THE EXCAVATING SPONGES. 337 



Hebridean Seas, read at the Meeting of the British Asso- 

 ciation at Nottingham, and will be published in the forth- 

 coming Report. 



The following is the genus and a list of the species named in 

 honour of Mr. Alder. 



Genus. Alderia (Allman), a genus of Nudibranchiate Mollusca. 

 Species. Natica Alderi (Forbes). 



Jeffreysia Alderi (Carpenter). 



Rissoa Alderi (Jeffreys). 



Eolis Alderi (Cocks). 



Bicellaria Alderi (Busk). 



Aysidota Alderi (Busk). 



Montacuta Alderi (Bate). 



Megamsera Alderi (Bate). 



Corynopsis Alderi (Hodge). 



Polyenia Alderi (Forbes). 



Zoanthus Alderi (Gosse). 



Isodyctya Alderi (Bowerbank). 



Cliona Alderi (Hancock.) 



XXXI. — Note on the Excavating Sponges, with Descriptions of 

 four new Species. By Albany Hancock, F.L.S. (Plates 

 XYI, XVII.) 



Since the publication of my paper on the excavating sponges"'-' 

 I have re-examined nearly all the species therein described, and 

 have carefully investigated several new and interesting forms 

 from various parts of the world ; and as a result of these re- 

 searches, I have only become more confirmed in the opinion, that 

 these lowly organized creatures are endowed with the power, of 

 whatever nature it may be, of forming the crypts and channels 

 in shell and other hard calcareous bodies within which they lie 

 concealed. The means by which this work is achieved is still, I 

 frankly admit, involved in much obscurity. 



* Ann. ami Mag. of Nat. Hist., 2nd Series, Vol. Ill, p. 321. May, 1849. 



