302 Messrs. W. K. Parker and T. Rupert Jones on some 



larity. The aperture in the nautiloid forms is usually near the 

 lower part of the chamber, but occasionally almost central ; it is 

 large, usually transverse and semilunar ; frequently jagged in 

 outline or irregularly lobed, and occasionally compound (therein 

 approaching that of Lituola, which, with its divided chambers, 

 is to Placopsilina * as Orbiculina is to Peneroplis) . 



The aperture in the straight part of the crosier-shaped indivi- 

 duals is central and usually round. In all cases the aperture is 

 faintly lipped. 



The chambers (as usual in the non-hyaline Foraminifera) are 

 set one on another by their edges, like tents or inverted cups, 

 not like bladders or bottles ; and, when the animal grows in the 

 fixed condition and is flat, the chambers are more or less deficient 

 of substance on the attached side. In the attached form it is 

 Truncatulina-like at first, but passes off into an irregular serial 

 gi'owth of transversely broad but unequal chambers. 



A characteristic of the recent specimens is the yellow or fer- 

 ruginous tintf of the shell, arising from the colour of the sandy 

 particles which enter so largely into its composition. 



Either in the nautiloid or the crosier-like forms, this shell is 

 known to us in the Oxford Clay, Gault, Chalk-marl, and Chalk ; 

 and authors quote it from the Chalk of Europe, the Tertiary of 

 Coroncina (Italy), of Hermsdorf (near Berlin)^ and from existing 

 seas. The fix6d forms occur abundantly in the Jurassic J and 

 Cretaceous deposits. 



EXPLANATION OF PLATES X. and XL 

 Plate X. 



[All the figures (except fig. 12) are magnified about 12 times linear.] 



Fig. I. Cristellaria Calcar ; attenuated variety. 2. The same; edge-view 

 of last chamber. 



Fiff. S. Dentalina commimis ; fragment. 4. Last chamber of another spe- 

 cimen. 5. The same ; external aperture. 



Fig. 6. Nodosaria Icevigata. 7. The same; external aperture. 

 Figs. 8, 9. Nodosaria Icevigata ; varieties. 



Fig.\0. Cristellaria Calcar. 11. The same; edge-view. 12. The same; 

 external aperture ; more highly magnified. 



, * Placopsilina may be said to represent, among the non-hyaline Fora- 

 minifera, the Acervulina among the hyaline forms. 



t This yellow tint characterizes also the so-called Nonionina pelagica, 

 D'Orb. (Voyage Amer. Merid. vol. v. part 5. pi. 3. f. 1.3, 14), which is appa- 

 rently closely allied to P. Canariensis, but far more gibbous, with inflated 

 and rapidly enlarging chambers. 



X It is abundant on the Ostrcea Marshii of the Inferior Oohte near 

 Peterborough. 



