Mr. H. J. Carter on the Polytremata. 209 



section of the Kelat fossil {Alveolina meandrina) , to which 

 I have above alluded as closely allied to Mr. Brady's de- 

 scription and illustrations of Lqftasia^ there was no appearance 

 of sand-grains ; I therefore became suspicious of the so-called 

 " arenaceous " composition. Ilence I examined my specimen 

 of Parker ia with this view, and find that the fibre of the reti- 

 culated structure is composed of transparant colourless calc- 

 spar, covered with a rough or frosted yellowish granular coat 

 of calcareous material, more or less filling up in larger crys- 

 tallization of the same form some parts of the labyrinthic 

 interstices (much as stalactite in a limestone cavern, &c,). 

 I therefore infer that the original fibre is represented by the 

 calcspar, and that the granular coating has been added during 

 fossilization. Had the latter been siliceous instead of calca- 

 reous, it would probably have presented the usual smooth, or 

 at least prismatoid, granular appearance of botryoidal chalce- 

 dony, instead of the rough rhombohedral granulation of a cal- 

 careous base ; so that the " sand-grains " so well represented 

 by Dr. Carpenter in the siliceously infiltrated specimen {torn. 

 cit. pi. Ixxvi. fig. l),if also composed of silex like that of the 

 infiltration, should, it seems to me, be viewed as a siliceous 

 pseudomorph of calcareous crystallization. 



It is almost impossible to conceive a hard, sharp, granular, 

 angulated surface in any organic cavity where the soft parts 

 in contact with it are in continual motion, as it seems im- 

 possible to confound the heterogeneous sand-agglomeration 

 so often witnessed in Foraminiferal tests with the uniformity 

 of this mineral crystallization. In a specimen of Lituola 

 nautiloidea^ Lam. {canariensis, D'Orb., raihi), about one sixth 

 of an inch in its greatest diameter, this contrast is most 

 obvious ; while the " labyrinthic " structure is cancellous 

 laminar, like that of bones, and not composed of reticulated 

 fiby-e like that of plants and Parkeria. In Lituola the laby- 

 rinthic structure is excavated tn the test ; in Parkeria the 

 reticulated fibre, in which the " labyrinthic system " is, is the 

 test itself. 



I have alluded to the absence of the foraminated area? ; but 

 I think I can see one of these on the border of the " conical 

 space ^' in my mounted section, in which the foramina and their 

 regularity in size (l-1800th inch in diameter) and position 

 are almost identical with those in the interstices of the reti- 

 culated structure oi Polytrema balaniforme^ and therefore much 

 smaller and more regular than any thing of the kind pre- 

 sented by the reticulated structure generally of Parkeria : 

 hence the openings of the labyrinthic system, as this structure 

 was successively formed on the surface of the concentric layers 



