160 On a Species of Arenaceous Foraminifer (^) . 



have spread out over the rock in tlie same manner as we ob- 

 serve in the recent sponges. 



I have said above that the interstices between the stolons 

 or labyrinthiform structure are filled with sand, and from its 

 appearance and hardness I thought it was quartz, as it is much 

 harder than the limestone or calcareous matter which fills the 

 stoloniferous structure, and resisted the action of the acid so 

 thorouglily, while the interspaces were quite eaten away, 

 that walls of crystals, as they now prove to be, were left 

 standing up round the interspaces. My friend Mr. Vicary 

 has kindly submitted a fragment of this fossil to the blowpipe, 

 when it burns into a white lime, with minute scattered points 

 of a metallic substance resembling iron, probably a carbonate 

 or sulphate of iron. It is this, no doubt, which has given the 

 crystals a ferruginous tint. 



It has struck me as very cm'ious, since it has been disco- 

 vered that the crystals are calcareous, and, from their rhomboid 

 form, they are believed to be carbonate of lime. If this be really 

 the case, it would seem that this was an animal secretion. 

 The crystals are very irregularly deposited, and adhere to 

 each other at various angles ; they are nearly all of the same 

 size. I have met with similar crystals on the membranes or 

 chitinous matter in the shells of Carcinus mopuas ; and they 

 are also found in the shells of oysters, on the animal secretions ; 

 it is therefore not singular that they should be found here, 

 and more particularly as both the Spongiada? and the Forami- 

 nifera secrete calcareous or siliceous matter as the case may 

 be. The crystals measure -gV of an inch in diameter, vary- 

 ing but little in size. If these grains, or crystals as they 

 now prove to be, had really been quartz, as I at first consi- 

 dered they were, I should then have thought that I had 

 a new form of Cliona before me, and that it had the habit 

 of constructing an arenaceous covering for itself. It may be 

 thought by some, perhaps, that this was a burrowing CUona.y 

 and that the infiltration of the calcareous matter into the sto- 

 loniferous structure may have quickly succeeded the death of 

 the animal, and what are now crystalline rhomboidal prisms 

 may have succeeded the decay of the rock or shell in which 

 the Cliona lived and died. But I do not think this can 

 have been the case. In the first place, the thickness is 

 against it ; and in the next, what should have precluded 

 the infiltration into the decaying shell (an assumed shell) 

 of the same material as that which fills the labyrinthiform 

 or stoloniferous structure ? I know of nothing ; and I think, 

 therefore, that we must fall back upon the supposition that 

 this animal secreted the carbonate of lime. I scarcely know 



