AND STEUCTUUE OF THE BELEMNITE. 407 



usual white limestone. When inclosed in flint, the shell still 

 remains in the same state, and, as Laumont has observed, the 

 interior and exterior flint are connected at the vent of the ani- 

 mal, and when the carbonate is removed by means of acid, the 

 flint appears to have penetrated all the minute pores, and 

 presents sharp and prickly ridges along the different lobes or 

 portions of which the shell of the echinite is formed. 



The Belemnite is a very common fossil, yet, for the sake of 

 perspicuity, it is necessary to describe it in a particular man- 

 ner. 



It occurs in great abundance in the south of England ; and 

 although Parkinson and others describe several varieties, the 

 belemnites of Antrim appear to me to be only of one kind, 

 pretty much of a size-, measuring in general about three or 

 four inches in length, and from half an inch to three-fourths 

 in thickness. The form is that of a cylinder, terminated at 

 one end with a conical point, furnished with a slender process, 

 of about a quarter of an inch in length ; but it is only when 

 the belemnite has been inclosed in flint that this delicate 

 member has been preserved. At the other extremity, the fos- 

 sil is always more or less broken, and provided with a cavity 

 or alveolus, which is filled up with the material in which it has 

 been imbedded. This cavity is conical, terminating with a 

 sharp point, and occupies a situation a little to one side of the 

 centre of the cylinder. 



In composition, the belemnite, whether inclosed in lime- 

 stone, flint, clay or sandstone, is uniformly formed of cristal- 

 lised carbonate of lime, striated and radiating to the circum- 

 ference, from a line which passes from the apex of the alveo- 

 lus to that of the fossil. 



In colour it varies. Those that are found in strata where 

 clay abounds, are opake, and of a dark-brown ; while those 



VOL. IX. p. II. 3 F that 



