191 



December 21, 1854. 



The LORD WROTTESLEY, President, in the Chair. 

 James Allman, M.D., was admitted into the Society. 

 The following communications were read : 



1. " Remarks on the Anatomy of the Macgillivrayia pelagica 

 and Cheletropis Huxleyi (Forbes); suggesting the esta- 

 blishment of a new genus of Gasteropoda/' By JOHN D. 

 MACDONALD, R.N., Assistant-Surgeon H.M.S. Herald. 

 Communicated by Sir W. BURNETT, K.C.B. &c. Re- 

 ceived November 23, 1854. 



Having examined the anatomy of the Macgillivrayia pelagica and 

 several smaller species of pelagic Gasteropoda, not exhibiting the 

 least similarity in the character of their shells, the author found that 

 they all presented a very close relationship to each other in the type 

 of their respiratory organs, and in other points of structure of less 

 importance. 



The gills in every instance seemed to be fixed to the body of the 

 animal immediately behind the head, and did not appear to be ap- 

 pended to the mantle, as in the Pectinibranchiata properly so called. 

 They were also invariably four in number, and arranged in a cruci- 

 form manner round a central point. They were free in the rest of their 

 extent, elongated and flattened in form, with a pointed extremity, 

 and fringed with long flowing cilia, set in a frilled border. They 

 were, moreover, furnished with muscular fibres, both transverse and 

 longitudinal, and exhibited great mobility when protruded, but lay 

 side by side in the last whorl of the shell when retracted. 



The auditory capsules, each containing a spherical otolithe, were 



VOL. VII. X 



