146 PICTURESQUE SKETCHES 



fish is an example. Another form, still more re- 

 markable, is met with in a fossil state, and includes 

 a vast number of species strictly confined, like the 

 true ammonites, to the secondary period. It is 

 known by the name of Belemnites, * and is a most 

 characteristic and abundant genus. 



The cuttle-fish has been already described as pos- 

 sessing a kind of calcareous skeleton, so ingenious- 

 ly contrived, (being formed of numerous stages of 

 thin calcareous plates, kept apart from one another 

 by the interposition of millions of microscopic pillars,) 

 as to serve as a float instead of impeding the motions 

 of the animal. Rendered in this way as light as the 

 water in which it dwells, the animal moves rapidly 

 along, either backwards by forcing water through a 

 tube, or forwards by the aid of a long pair of flat, 

 broad tentacles, projecting beyond the eight arms 

 which surround its head. At the approach of danger 

 it is enabled to sink suddenly ; and at the same time 

 it throws out, from a singular receptacle called an 

 ink-bag, a quantity of dark-coloured fluid, in the 

 obscurity caused by which it is better able to es- 

 cape from its enemies. 



The belemnite has been long known as a solid 

 calcareous fossil, of a conical shape, more or less 

 elongated ; and it was also known, that, while the 

 pointed end of this fossil was solid, the other ex- 

 tremity enclosed a number of plates like watch- 

 glasses, fitting into a conical hollow. Specimens too 

 had been found, especially in the lias, where a consi- 

 derable portion of thin horny sheath extended beyond 

 the ordinary termination of the shell, and beyond the 



* BsXs^vav (belcmnon), a dart. 



