1835.] of Pelagian Shells, taken on a voyage to India. 175 



the centre and base, and is broader than that of Atlanta : the tentacula 

 are much smaller in proportion, and the centre of the spire is occu- 

 pied by the dark brown mass of the liver : whereas in Atlanta this 

 part appears to be filled with a series of forms resembling ova. 



Tbe shell differs principally in having whorls closely convolute, and 

 partly enveloping the preceding ones ; while in Atlanta, the whorls are 

 loosely rolled*, and the keel (which stops short at half the circumfer- 

 ence in Oxygyrus) runs on between the whorls, and connects them 

 together. In Atlanta the form of the mouth, which is entire, is ellip- 

 tical, with an operculum of the same shape. In Oxygyrus the oper- 

 culum is cordiform, corresponding to the form of the aperture, and in 

 the only species yet discovered the shell is cartilaginous, while in 

 Atlanta it is testaceous. This cartilaginous shell shrinks in drying, 

 particularly the last whorl, the centre ones appearing to be of firmer 

 consistence. In the species described, the shell is tumid, herein widely 

 differing from the very compressed and flattened form of Atlanta. 



Having sketched the animals of both shells while alive, under the 

 lens, I can speak confidently regarding their affinity, which I had 

 noted as probable, before I had an opportunity of examining the 

 animal of the new genus. 



Like Atlanta, the animal moves by sudden starts, quickly agitating 

 its swimmer. It occasionally adhered to the bottom of the vessels in 

 which it was placed, by its sucker, which then was flattened out to 

 the surface to which it adhered. 



We first met with the shell in the Southern Atlantic from S. Lat. 

 15° to 20° 30' and between W. Long. 29° 30' and 23° 30'. In the 

 Southern Indian Ocean, we again met with it in 29° 30' S. Lat. and 

 32° E. Long., and it continued to occur at intervals up the Bay of 

 Bengal to N. Lat. 17° and E. Long. 87°. It has therefore a very 

 extensive range of sea and climate, and I am surprised that the French 

 naturalists, who have of late swept the seas with so much zeal and 

 success, have not met with it. 



The animal comes up to the surface, with the Pteropodous mollusca 

 and the Firolidee, shortly after sunset, and may then be taken with 

 the tow-net. With this apparatus I was extremely successful, during 

 my late voyage from England, in procuring Pelagian shells, as the 

 following catalogue will shew. My example being followed by two 

 other passengers, we allowed but few objects on our route to escape 

 us. I was also enabled, with a throwing-net, to capture such large 

 shells as were visible from the poop, and which would have otherwise 



* Note. — Oxygyrus bears to Atlanta nearly the same relation that Orbulites 

 does to Ammonites. 



