17*2 



14. Baculites, — A raultilocular straight, or slightly bent, 

 cylindrical, or slightly conical, shell ; the chambers sepa- 

 rated by sinuous septa, pierced with a marginal siphuncle. 

 Fossil. — PI. vi. fig. 10. 



13. Belemnites. — A conical or fusiform stone, of brown 

 radiating spar, generally terminating at the small end in a 

 point, and having at the larger end a conical cavity, natu- 

 rally retaining a conical testaceous body, divided into cham- 

 bers by plain concave septa, and pierced by a siphuncle. 

 Fossil. — PI. vi. fig. 11. 



16. Hippuritcs. — A straight or conical shell, furnished 

 internally with transverse septa, and with two lateral, longi- 

 tudinal, obtuse, and converging ridges, of very light texture. 

 Fossil.— PI. vi. fig. 12. 



It was endeavoured to show, in a former work, that the 

 spathose substance in the belemnite was originally a light 

 substance, of a texture somewhat similar to cork, and was 

 the float to the animal, which rendered it so nearly equal to 

 the weight of water as to allow it to rise or fall, as the 

 siphuncle was filled with air or with water. 



In the fossil last described, a peculiar modification of 

 structure in its covering appears to have accomplished the 

 same purpose : the shelly enclosure has evidently been of a 

 peculiar light texture, by which such a diminution of the 

 gravity of the mass would be obtained as would fit it for 

 being similarly acted upon by the internal presence of gas 

 or of water, as in the instance of the belemnite. 



17. Tiirrilites. — A spiral, turriculated, multilocular shell; 

 the turns contiguous, and all visible ; the chambers separated 

 by winding septa ; with a siphuncle in their disks ; the 

 aperture round. Fossil. — PL vi. fig. 13. 



18. Fasciolites, — A subcylindrical shell, formed of multi- 

 locular tubes, narrowing at both their ends, disposed con- 

 tiguously and parallel ; the tapering ends transversely andl 

 obliquely folded on each other. Fossil. — PI. vi. fig. 14. 



