296 Messrs. W. K. Parker and T. Rupert Joues on some 



Tertiaries. In this case, numerous individuals exhibit a gradual 

 replacement of the cone by a trihedral (Vcrneuiliua-like) series 

 of chambers, which are ultimately produced collaterally and un- 

 equally in a spiral (Bulimina-like) arrangement, and exhibit a 

 terminal fold-like aperture protected by an opercular tongue 

 (as in Valvulina). 



Tliis interesting species, which is a trochiform Textularian 

 Rosalina in its young state (figs. 15 & 16), and presents a 

 combination of Verneuilina and Bulimina in its advanced growth, 

 appears to have only the Valvuline condition of its aperture as a 

 permanent character throughout*. 



D'Orbigny^s V. triangularis (illustrated by his Modele, no. 25) 

 is this form at an intermediate stage, when the Verneuilina has 

 prevailed over the Rosalina, and begins to lose its triangularity 

 previously to being superseded by the Bulimina. 



21. Bulimina marginata, D'Orb. PI. XI. figs. 35-40. 



Bulimina marginata, D'Orb. Ann. Sc. Nat. vii. p. 269. no. 4. pi. 12. f. 10-12. 

 Bulimina ovula, D'Orb. Voy. Am. Merid. Foram. pi. 1. f. 10, 11. 

 Bulimina caudigera, D'Orb. ib. p. 270. no. 16; Modeles, no. GS. 



Shell varying from ovate to fusiform, formed of numerous 

 chambers arranged alternately on a ternate plan, and affecting 

 somewhat a spiral arrangement. The earlier chambers much 

 less in size than the later ones, and sometimes obscured by their 

 excessive backward overlapping (as in figs. 36 & 37 ; still more 

 so in B, caudigera, D'Orb.). The larger and later chambers are 

 subglobose or somewhat oval in their external outline. The 

 aperture is distinctively a little loop-shaped niche, formed, as it 

 were, by the folding- over and convergence of the two halves of 

 the extremity of the chamber; it is sometimes provided with a 

 little, narrow, internal, tubular neck. 



The shell, in the small varieties here figured, is hyaline and 

 very diaphanous. In larger individuals the shell becomes thicker, 

 coarsei-, and densely studded with sand-grains. The external 

 ornament appears to be generally confined to the fringing of the 

 posterior portion of some or all of the cells with prickles of variable 

 size, and of very inconstant occurrence on nearly all the varieties. 

 In figs. 39 & 40, this fi'inging is well shown, and the shell of 

 this most-prickled variety is stronger than the others ; whereas 

 in the ovate and elongated forms (figs. 35 & 36) the shell is of 

 extreme tenuity ; certainly as thin as in any Foraminifera we 

 have yet examined. The emaciated variety, fig. 35, does not put 

 on prickles. 



* Clavulina appears to afford an analogous interchange of structural 

 types ; but it ultimately takes on a Nodosai'ian, instead of a Bulimina-likc 

 groutli; retaining a Valvuline ajierture. 



