484 FOSSIL INVERTEBRATED ANIMALS. 



first presents, in general, the form which we have just men- 

 tioned. Sometimes it is rounded towards its extremity, and 

 then terminates in a small point. At other times it is swelled 

 in two-thirds of its length, and resembles a spindle. It may 

 also be flatted on the sides, and present lateral ridges. In 

 general it is hollowed at its surface, which is smooth, with a 

 longitudinal furrow. When it approaches the cyKndrical form, 

 the interior is marked with a circular striae, or ribs. On being 

 broken transversely, it presents a sort of crystallization com- 

 posed of needles, which proceed radiating from the axis of the 

 cone towards its circumference. On its being divided longi- 

 tudinally, these needles incline towards the summit a little. 

 But we observe, at the same time, in this section, chiefly in 

 the cases of belemnites which have been polished, a series of 

 longitudinal lines which set out, two by two, from the axis 

 under a very acute angle and direct themselves towards the 

 base. They indicate a series of layers or cornets of stony mat- 

 ter, inclosed, as it were, one in the other. The case has, in 

 its interior, a conical cavity, which extends, in the most 

 entire belemnites, as far as the moiety of its length. Some- 

 times it has them but for a third. This cavity is exactly filled 

 by the alveolus, formed by an union of cells, the number and 

 extent of which vary much, according as the partitions or 

 septse which intercept them are more or less distant one from 

 the other. There are also four small kind of caps, the con- 

 vexity of which is directed towards the summit of the cone ; 

 their centre is sometimes pierced by a siphon, or canal, which 

 at other times is on one side. It traverses all the small cells, 

 and communicates only with that of the base or the last, as 

 is the case with the nautiU, or ammonites. 



It is rare to find belemnites with their alveoli. But they 

 are extremely common without this part, which is also found 

 separately, but more seldom. The majority of naturalists 

 who have spoken of these bodies have not seen them together 

 ' — from this has arisen the variety of opinions advanced upon 



