GENUS CALCAKINA : INTEENAL STKTJCTTJBE. 553 



of the newest whorl is covered with punctations resembling those of the general surface 

 of the disk ; but they are more minute and more closely set together, and they are dis- 

 tributed with great uniformity, no unpunctated spaces being anywhere visible. 



202. Internal Structure. When the internal structure of this organism is examined 

 by means of thin sections taken in different directions, the apparent anomalies of its 

 conformation are found to be dependent simply upon the extraordinary development of 

 its " supplemental skeleton;" its general plan of structure being much simpler than the 

 peculiarities of its aspect would seem to indicate. The spire, as laid open by vertical 

 section (Plate XX. fig. 1), is turbinoid ; consisting usually of about five whorls (, a 1 , a 2 , 

 a 3 , a 4 ), that start as usual from a central cell, and progressively increase in size, each 

 whorl being applied merely to the surface of the preceding, and not investing it in any 

 degree, the chambers being altogether destitute of alar prolongations. The aspect of 

 the spire as seen in equatorial section is shown in Plate XX. fig. 4 ; this section, being 

 taken in such a plane as to cut through the outer whorls a 4 , a 3 , a 2 , passes entirely over 

 the surface of the two inner whorls a 1 and a. The disposition of the chambers, as indi- 

 cated by such sections, is ideally shown in Plate XIX. fig. 12. The turns of the spire 

 are separated from each other by the interposition of a thick layer of solid shell-sub- 

 stance ; and this is quite distinct from the proper walls of the chambers, as may be well 

 seen in Plate XX. fig. 4, where the walls of the newest chambers are shown at b to be 

 entirely destitute of any such addition, whilst at b } in the preceding part of the same 

 whorl we observe them encrusted by a thin additional layer d, and, as we trace this layer 

 backwards to d l and d 2 , we perceive that it progressively augments in thickness, until it 

 acquires its maximum at d 3 , just where it is covered by the subsequent whorl. This 

 distinction between the proper walls of the chambers and the " supplemental skeleton " 

 can be traced to the very centre of the spire. The septa are entirely formed by the 

 infolding of the proper walls of the chambers, which are there flattened against each 

 other so as to form two layers, which are usually in contact, but which sometimes 

 diverge (especially near the external margin of the chambers) to give passage to canals. 

 There does not appear, however, to be any regular " interseptal system " as in Oper- 

 culina and Polystomella. The communication between the adjacent chambers of the 

 same whorl is effected, as in Polystomella, through series of pores (fig. 1, c) disposed at 

 pretty regular intervals along the inner margin of the septum*. 



203. That the spines entirely originate from, and are strictly appendages of, the 

 "supplemental skeleton" is well seen in fig. 4, which shows their connexion with its 



* Messrs. PARKEE and JONES say (Ann. of Nat. Hist. Ser. 3. vol. v. p. 175) of the aperture of Calcarina, 

 that " in well-preserved specimens of the typical forms, the real aperture, which is essentially a slit, as in the 

 true Botalite, becomes bridged over by delicate bars of shell-matter." I cannot but think that they have 

 allowed themselves in this statement to be somewhat influenced by a foregone conclusion that " Calcarina 

 is a subgenus of Botalia." The examination of numerous sections of the character represented in fig. 5 

 leaves no doubt in my own mind that the aperture of Calcarina is essentially such as I have above described ; 

 and that if it occasionally in perfect specimens has the character of a continuous fissure (which I would by 

 no means take upon myself to deny), such is an aberrant rather than the ordinary form. 

 MDCCCLX. 4 D 



