312 PHILOSOPHICAL TRANSACTIONS. ' [aNNO 1747- 



matter, with an intermixture of spar or crystal, disposed in striae from or near its 

 centre to its circumference, and is made up of crusts inclosing each other, the 

 innermost being as regular as the outermost. Sometimes, though seldom, in 

 comparison to the numbers of the belemnites, in the centre is a cavity, always 

 conical, whatever the external shape of the belemnites be. This conic cavity is 

 at different times empty, or else filled, either with a solid body of mineral matter, 

 crystal, stone, pyrites, &c. or with a regular jointed conic body, called by litho- 

 logists the alveolus of the belemnites ; whifch, though constantly regular and 

 jointed, is yet composed of various mineral or metallic substances. 



The alveolus, though not fully proved such, yet seems, by the assent of most 

 of the present naturalists, to be a body of marine origin ; a shell the nearest re- 

 lated to the nautilus kind : it is concamerated, and even in some is discovered 

 another great characteristic of the nautilus kind, viz. the gut or siphunculus. 

 Therefore, taking this body for granted to be of marine origin, it remains to dis- 

 cuss, whether th*s body became accidentally lodged in the belemnites ? or, 

 whether the belemnites itself is also of marine origin, and a part dependent on 

 its alveolus ? 



Various have been the opinions of lithologists concerning the origin of the 

 belemnites ; some have even asserted them of the vegetable kingdom ; others, 

 that they are teeth or horns of fish, appendages of shells, bodies cast in shells of 

 the tubuli kind, or the very shells themselves, spines of echini, or a kind of 

 straight nautilus. The last 3 opinions are what he endeavours to confute, as 

 they seem somewhat probable, and are now the most prevailing ; and to prove the 

 belemnites to be a natural fossil or lapis sui generis. 



Tliat the belemnites are not teeth or horns of fish, is shown in the letter Dr. J. 

 Woodward wrote on that subject to Mr. Bourguet, of Switzerland. But a fur- 

 ther argument against their being teeth, which that learned naturalist has not 

 touched on, is, that no belemnites have their natural varnish or polish, which 

 always covers the teeth of all animals ; whereas the greatest part of those fossil 

 bodies, which we know to be such, as the bufonitae, glossopetrae, &c. are found 

 with that same varnish or polish. As for their owing their form to being moulded 

 in shells, it will appear contradictory to reason, when we consider, 1st, that their 

 constitution is always as regular as their figure ; and, 2dly, that their inner layer 

 or nucleus is as equally regular as the outer crust or whole body ; which particu- 

 lar could never have happened, had they been moulded in shells ; as is evident, 

 by the turbinitise, conchitae, and other bodies, which owe their figures to that 

 cause. That the belemnites are not spines of echini, let us first consider, that 

 no kinds hitherto discovered have ever been found with spines analogous to these 

 bodies ; nor indeed has any marine shell whatever such a texture. 



He is sensible there are some species of fossil echini ; as, the most common 



