and on the shell of Sphcerulites. 229 



When one of these shells is cut across in the axis of the cone, it 

 is then found that the transverse laminae are continued, and the 

 cells which appeared regular in the longitudinal section, are seen to 

 be rather irregular in size and form, but mostly hexangular or pen- 

 tangular. They are deposited on these transverse plates, the next 

 transverse plate or lamina of growth being laid over them ; and as 

 the cells of the next and every succeeding series are exactly simi- 

 lar in form and numbers, there necessarily results that uniformity 

 which we have mentioned in the appearance of the longitudinal 

 fracture, since the parietes of the cells of the different transverse 

 laminae appear in that fracture to be as much continuous with one 

 another as the transverse ones really are. An analogous peculiarity 

 exists in some shells of other structures. Thus in the Pinna, and 

 other shells of a prismatic crystalline structure, the transverse prisms 

 of which the outer coat of the shell is formed, appear to be con- 

 tinuous, though they are each formed of the many transverse laminae 

 of growth which are in succession deposited as the animal enlarges 

 its size : and it is the same with the rhombic crystalline structure. 



The outer surface of this shell (Spheerulites) is lamellar and hard, 

 being formed by the agglutinated outer edges of the transverse 

 laminae of growth ; and the inner surface of the cone is covered with 

 a thin hard plate, which is marked with minute close concentric lines 

 more numerous than the transverse plates of the parietes of the 

 shell ; and the plate is raised at the mouth of the cone a little above 

 the surface of the lip, from which it is separated by a slight groove. 



The mouth of the lower cone has a smooth concave lip as wide, 

 or rather wider than the thickness of the parietes of the shell, and 

 is marked with some radiating branched impressions, exactly like 

 the impressions which one may suppose to be made by a blood- 

 vessel j the slenderer and branched part being directed towards the 

 outer edge of the lips. 



A similar structure is to be observed in other species of this genus 

 fossilized in limestone, but from the size of the cells in these, as 

 appears when specimens of the same magnitude are compared, it is 

 obvious that the whole formation was on a much smaller scale ; and 

 the cells are always filled with infiltrated carbonate of lime, which 

 makes them appear solid, unless the surface of the specimen is 

 slightly disintegrated, or the fracture is wetted and examined with 

 a lens. 



I can scarcely attempt to explain how the parietes of these cells 

 are formed, nor determine if any fluid has, in their living coudition, 



VOL. II. no 9. Q 



