and on the shell of Sphcerulites. 231 



present in the species under examination,) it must have been lost 

 before the shell was submitted to the fossilizing process, since other- 

 wise the holes could not have been drilled into, nor the oyster shells 

 attached to, the surface. 



A somewhat similar structure or appearance is to be observed in 

 some Madrepores, especially in the spaces between the sinuous com- 

 pressed stars of Meandrina, but in these zoophytes the longitudinal 

 places are continuous and first deposited, and the thin transverse la- 

 minae are interrupted and irregular, instead of forming the conti- 

 nuous plates which they do in the Sphserulites. 



Some naturalists have compared the structure with that of Conia 

 and the barnacles, but this must have originated in a very super- 

 ficial view of the matter, for the valves of the barnacles are pierced 

 with conical tubes gradually tapering from the base to the apex of 

 the valve, and they are not cellular but tubular. The base of some 

 barnacles is indeed cellular, and somewhat resembles the structure 

 in question, but in them the longitudinal or rather radiating plates 

 are continued, and the transverse ones, when present, unequal and 

 disposed irregularly in different directions, showing even a more ir- 

 regular cellular structure than in the Meandrinae before referred to. 



II. The second form of this structure is found in a recent unde- 

 termined species of oyster which I do not know in a perfect state. 

 This shell exhibits the usual lamellar structure of its genus, but the 

 laminae of growth, which give the peculiar antiquated appearance 

 to the common oyster, instead of beiiig left free, are bent down so 

 as to produce a nearly even outer surface. When these laminae are 

 broken through, it is ascertained that the spaces under them are 

 filled with a soft purplish spongy mass, composed of minute, rather 

 irregular cells, placed perpendicularly between the plates. When 

 these are near together, the cells extend from one plate to the other, 

 but when they are wider apart, the cells are sometimes interrupted 

 in the centre. They have somewhat the appearance of being casts 

 of the interstices between the prisms of the prismatic structural 

 shells, and are deposited in layers as the other parts of the shell are. 

 I think they may be analogous to the opaque white chalky matter 

 often found interposed between the laminae of the common oyster, 

 but here, though the chalky matter is sometimes seen on the inside 

 of the exterior imbricate foliations, as the cellular structure is found 

 in the shell under more immediate consideration, yet it is to be ob- 

 served more abundantly, and commonly forming a convex spot in 

 the disk of the cavity of the oyster, just beyond the scar of the large 



