00 PHILOSOPHICAL TBANSACTIONS. [aNNO I764. 



Stons-field they are found much longer than at Piddington, and are enclosed in 

 stone, which is split by the workmen to make slates. Here they are often 

 found in a much more perfect state, (fig. 1,) than the former, with the alveolus 

 in many of them ; but that part is commonly crushed (ibid at y) by the incum- 

 bent matter. 



The siphunculus of the belemnite is always on the- verge of the chamber, or 

 cell ; and in the siphunculus is a little gut or duct, proceeding from the body of 

 the animal, by dilating or contracting of which, the animal, it should seem, may 

 go out or into its cell at pleasure. This is the only stay which the animal has to 

 secure its retreat : but he cannot agree with the learned doctor Hooke,* that 

 the gut or duct passes through all the cells to the end of the spiral cone, either 

 in this shell or the nautilus. His discovering of a spiramentum in the centre 

 of the latter was merely conjectural ; for the ends of the spiral cone of con- 

 camerated shells-|- are shut up in the same manner with those of the turbinated 

 kind ; and it is common for all turbinated shell-fish as they increase in bulk, 

 and enlarge their shells, to leave their bottom or first-formed convolutions. 

 Therefore Mr. P. makes no doubt but the same is done by the concamerated 

 tribe ; for if the gut go through only one or two valves, it will be a sufficient 

 stay to the animal, and, being contracted or dilated, will serve all the purposes 

 above mentioned. How far this is practicable by our little inhabitant, cannot 

 absolutely be determined ; but if it be constantly fixed by the gut to the siphun- 

 culus, it has a surprising power of contracting and dilating its body, to extend 

 so far as the bottom or point of the belemnite, which in some is more than 30 

 times the length of the cell into which it returns (fig. 8). He thinks that this 

 gut or duct, as well as the body of the creature, is capable of being extended 

 very considerably to serve all the uses of forming the belemnite, without leaving 

 the siphunculus ; and that the gut serves for the same purposes with the tendons 

 of the oyster ; the latter to open and shut the shell ; the former to allow the 

 animal to go out and in at pleasure. And as the oyster feeds altogether in the 

 shell, by opening the verge, the belemnite (whose residence is in the great deep, 

 which is seldom disturbed) very likely goes out in quest of food, but travels only 

 on the guard or rampart, leaving a trail behind, as all land snails do ; which 

 hardening into a testaceous substance, increases the dimensions of the outer 



different strata, abounding nnore or less with pyritical matter. Where no spar follows the acid, the 

 parts are carried away and lost in the interstices of the earth, and a mould or plasm is left, which 

 Steno calls an aerial shell. See his Prodromus, page 84. But where the spar abounds, it pervades 

 the whole substance, fills up the cavity, and assumes the true form of the shell ; and sometimes, 

 by bursting the pores, is so far substituted in the pjace of the original particles, that the several 

 diaphragms, with the siphunculus of the alveolus, are accurately and nicely preserved. — Orig. 

 * Hooke's posthumous works published by Derham, 8°- p. 306". 

 ^ See the little pearly cornu-ammonis shell. — Orig. 



