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March 22, 1855. 

 The LORD WROTTESLEY, President, in the Chair. 



The following communications were read : 



I. "Further observations on the Anatomy of Macgillivraya, 

 Cheletropis, and allied genera of pelagic Gasteropoda." By 

 JOHN DENIS MACDONALD, Esq., R.N., Assistant-Surgeon 

 H.M.S.V. ' Torch/ Communicated by Sir W. BURNETT, 

 K.C.B. Received February 22, 1855. 



The author states, that in a late voyage from Sydney to Moreton 

 Bay, specimens of Macgillivraya, Cheletropis and a few other genera 

 of minute pelagic Gasteropoda, apparently undescribed, were daily 

 taken in the towing-net, and afforded him an opportunity of more 

 precisely determining the mode of attachment of the ciliated arms 

 which he had at first presumed to be naked branchiae. 



In his former paper* it was stated, more particularly of Cheletropis 

 Huxleyi, that the gills were of two kinds, viz. " covered " and 

 "naked;" the former, corresponding to those of the pectinibranchi- 

 ate Gasteropoda generally, he has never found to be absent in any 

 of the genera ; but from further observation of the so-called naked 

 gills, while the animals were alive in their native element, he is dis- 

 posed to think that they are chiefly employed for prehension, and 

 probably as auxiliary organs of natation. When these ciliated 

 appendages are fully extended, the line of cilia is perfectly straight, 

 so that the frilled border, noticed in the previous account, turns out 

 to be a character depending simply on the partial contraction of the 

 longitudinal muscular fibres, preparatory to complete retraction of 

 the organs. They have no connexion with the mantle, but encircle 



* Proceedings, p. 191. 



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