Orbitolites Mantelli, Gart.^from Burma. 347 



This I have never seen in any of my specimens of Orbito- 

 lites Mantelli, either from Arabia, Kelat, or Sind, nor in that 

 from Burma above described, while Dr. Carpenter himself 

 adds just afterwards : — " in the American variety of 0. 

 Mantelli I have not met with any indication of the presence 

 of these columns." 



Sometimes the columns of cells in Orbitolites Mantelli do, 

 in the vertical section, present a white appearance like the 

 " columns of non-tubular substance " in Orbitoides dispansa, 

 especially where the rest of the fossil is composed of dark 

 grey calcite ; but, then, the lighter-coloured correct the darker 

 specimens in this respect ; and if this does not suffice, we 

 have only to turn to the specimens of Orbitoides dispansa 

 and Orbitolites Mantelli, whose cavities respectively have 

 been infiltrated with red or yellow oxide of iron^ to see that 

 the cells in the former are accompanied by the opaque white 

 " columns of non-tubular substance ; " while in the latter 

 they are not so, but merely surrounded by the thin layer 

 of translucent shell-substance, through which, as before 

 stated, the '' canals "" — now rendered visible by being filled 

 with the oxide of iron — may be seen to connect the contiguous 

 cell-cavities. 



After all, Dr. Carpenter states at p. 299 [op. cit.) that 

 " There is so decided and constant a difference as regards the 

 form of the chambers between 0. Mantelli and 0. Fortisii, 

 that until such a gradational series of connecting links shall 

 be discovered as unites the similarly diversified varieties of 

 Orbitolites, they must be retained as distinct species." The 

 distinctive differences of Orbitoides Fortisii, Carp., = Orbi- 

 toides dispansa, Cart., and Orbitoides Mantelli=- Orbitolites 

 Mantelli, Cart., are as clearly given in his twentieth plate as 

 they are in my own, to which I have before alluded ; and 

 Giimbel, in 1869, makes the same distinction, proposing for 

 the latter the name '"'' Lepidocyclina^'' of which he states : — 

 " Mediankammern auf clem Horizontalschnitt peripherisch 

 halbkreisformig abgerundet. (Bei den vorhergehenden Unter- 

 gattungen [that is, Orbitoides dispansa &c.] dagegen rectan- 

 gular.)" — Biitschli, in Bronn's Klass. u. Ord. des Thierreichs, 

 1880, Rhizopoda, p. 216. 



To sum up, the central plane of Nummulites corresponds to 

 the form and arrangement of the plane of chambers in 

 Opercidiiia ; that of Orbitoides dispansa to the form and 

 arrangement of the plane of chambers in Cycloclypeus, Carp., 

 together with the initiative "cones of non-tubular substance" 

 as delineated in Dr. Carpenter's fig. 5, pi. xix. ; and that of 

 Orbitolites Mantelli to the form and arrangement of the single 



