^ PHILOSOPHICAL TRANSACTIONS. [aNNO I764. 



that no more convolutions could be carried on ; the indented lips being a full 

 stop to its inward dimensions ; and that here was the period of its growth. His 

 sentiments were just as to its inner dimension; but observing that the lips of 

 some were much larger than others, and that the curved part of the outer lip 

 appeared thicker, when sawed open, than the other parts of the shell ; he began 

 to think that the animal, instead of enlarging the inner dimensions, was em- 

 ployed in thickening the outer wall, to guard against injuries and accidents, 

 so common to the inhabitants of that turbulent element the sea. He was the 

 more confirmed in these sentiments by seeing the beautiful spots with which this 

 animal decorates its house, covered by other spots of different colour and size, 

 as new laminae were added to strengthen the last-formed convolution. It is 

 really matter of admiration to see how these shells are adorned and variegated ; 

 the exquisite polish which covers the whole infinitely surpassing the skill even 

 of the most accomplished human artist. These new coverings or laminae, 

 which are carried from the lips, terminate in the middle of the back part of the 

 shell ; and there form a list, or seam, of a quite different colour from that of 

 the other part of the shell, and of an unequal surface. 



This circumstance gave birth to Mr. P.'s sentiments concerning the formation 

 of the belemnite : for whoever considers the seam or fulcus in the belemnite, 

 will be apt to conclude that the outward lamina is formed latest, as in the 

 cowree, and that the seam or fulcus is caused by the several additional 

 coverings or laminae terminating there. But as the anatomist makes fresh dis- 

 coveries by dissecting the subject, so he received further information by luckilv 

 meeting with a belemnite, whose laminae were in a manner dissected and laid 

 open by the vague acid, or some other corroding menstruum, which every 

 where pervades the earth, destroying some bodies,* and forming others.-f- 

 The laminae of this truly wonderful body are here exposed to view, fig. 9, and 

 plainly show us, that nature in this, as in all her works, pursues the most simple, 

 easy, and shortest methods, though they appear ever so intricate and interwoven. 

 This specimen will serve to explain a matter which has so long puzzled the 

 curious in natural history ; and convince us that there is nothing more wonder- 

 ful in the formation of the belemnite than in that of a cockle, oyster, or any 

 other testaceous substance ; with this difference only, the oyster strengthens its 

 shell, and excludes its first habitation by additional laminae formed within ; the 

 belemnite incloses its dwelling by adding new laminae without. Fig. 10, repre- 

 sents the belemnite split up the middle, with the siphunculus in the front : a, b 

 exhibit the first formed cell, or seat of the animal ab ovo. As the animal grows 



• All calcareous substances. — Orig. 



+ Such as selenites, pyrites, marcasites, talc, gypsum, &c. — Orig. 



