Mr. H. J. Carter on the Polytremata. 199 



as they are successively formed between the layers of the 

 spiral Lamina, Avhich, winding round the hollow axis and 

 spreading out towards the base, at last ends in completing the 

 evolution of the conical test ; septa of the last-formed cavities 

 corresponding with the grooves on the surface. Presenting, 

 in horizontal sections at different distances from the base, sub- 

 concentric layers in a spiral form, diminishing in number up- 

 wards ; and in a vertical section, the same in a conical form 

 interrupted at the apices by the hollow columella. (For good 

 illustrations of this generally, see Dr. Carpenter's figures 

 alluded to in the " Explanation of the Plate.") Internal 

 cavities lined throughout by a structureless sarcodic layer, 

 which rests on the foramina of their Avails, and on becoming- 

 dry assumes a brown colour and chitinous aspect ; cavities 

 more or less filled with diiferent forms of siliceous sponge- 

 spicules, entire and fragmentary, together with grains of sand 

 (chiefly calcareous) and other minute objects, agglutinated 

 into a mass by a sarcodic (?) substance, which when dry 

 presents a dark brown colour. Test generally more or less 

 transfixed by siliceous sponge-spicules entire and fragmentary, 

 which become incorporated with the calcareous material during 

 its formation. Size about 9-24tlis inch in diameter at the 

 base by l-12th inch high. 



Hah. Marine, on the valves of MytilicarcUa calyculata and 

 other hard objects, Pecten^ Porttes, &c. {Cayyenter). 



Log. West Indies? Indian Ocean [Carpenter). 



Obs. Although the form and coloiu- of Po/^/^re/na balam'forme 

 are specifically different from those of P. mi niaceimi, the struc- 

 ture generically is the same ; that is, the subhexagonal reticu- 

 lation with foraminated interstices of the spiral layer, giving 

 in the horizontal and vertical sections subconcentric and conical 

 layers respectively, are mutatis mutandis the same ; while the 

 cancellated structure generally and the large internal cavities 

 containing more or less siliceous sponge-spicules and other 

 minute foreign objects, together with a superior opening, are, 

 but for their much larger size in P. balaniforme (bearing the 

 proportion of eight to one), almost identical — even to the 

 absence of the canal-system, which Dr. Carpenter uninten- 

 tionally confirms where he states respecting this system that 

 " the two layers [of the approximated chambers] sometimes 

 separate from each other, as shown in the figures, so as to 

 leave intraseptal spaces ; and these form a tolerably regular 

 canal-system, which may be traced throughout the network of 

 ridges that covers the inner wall of each principal chamber," 

 (fee. (Introd. p. 188). Now as the canal-system of a Forami- 

 niferal test is formed of distinct calcareous tubes^ through which 



