326 Mr. H. J. Carter on the Structure of the Foraminifera. 



completion, from the chamber just budding to that one extend- 

 ing from the margin to the umbilicus. This gradation is also a 

 consequence of age or full development of the Nummulite, there 

 being a gradual diminution in size from the largest chamber to 

 the primary one on one side, as there is from the largest to the 

 last-formed one on the other : hence the circular form of Num- 

 mulites. The same has been stated of Operculina ; but here the 

 termination is generally more abrupt, which causes the test to 

 assume a somewhat elliptical form. 



Classification of Nummulites. — On this subject I have but few 

 observations to offer, after the able one proposed by MM. d'Ar- 

 chiac and Haime (p. 72), viz. 1st, Laves aut Sublaves; 2nd, Re- 

 ticulata ; 3rd, Subreticulata ; 4th, Punctulata ; 5th, Plicata vel 

 Striata; and Gth, Explanata. What I have to state, however, 

 will be chiefly found under the descriptions of the species which 

 have elicited it respectively. 



The dividing of the Nummulites which present a reticulated 

 structure on the surface from the rest, which I proposed (Ann. Nat. 

 Hist. p. 1 G 1, 1853), was being carried into effect by MM. d'Archiac 

 and Haime for their second and third groups at the time I was 

 writing my MS. in India. So it is evident that I was not single 

 in suggesting this, — although I made a mistake, as they notice 

 (p. 343), in attributing the suggestion to Dr. Carpenter in the 

 first instance, whose proposition, on the other hand (Quart. 

 Journ. Geol. Soc. /. c. p. 30), was to make the Assilina a " sub- 

 genus" of Nummulites. But as regards MM. d'Archiac and 

 Haime's dividing the reticulated Nummulites into two groups, 

 and the changing of the name Assilina to Nummulites respect- 

 ively, I think it would have been better to have made but one 

 group of the former, as noticed by Messrs. Parker and Jones 

 (Ann. Nat. Hist.), and not to have changed the name of the 

 latter, for reasons which will be hereafter mentioned. 



Again, as regards my observation that the reticulated Num- 

 mulite N. acuta, Sow. "borders close upon Orbitoides," MM. 

 d'Archiac and Haime observe (p. 343), "II n'y a pas plus de 

 passage cntre cette Nummulite et l'organisation des Orbitoides 

 ( 0. dispansa) qu'entre tout autre corps de ces deux genres." I 

 was wrong certainly in stating that there was a commencing 

 degradation of the spire in N acuta into the horizontal plane of 

 Oi'bitoides, but no further; for, as will be seen, the external 

 appearance as well as the internal structure of O. dispansa ap- 

 proximates it to the reticulated Nummulites more than to any 

 other discoid Nummulite. Thus, the thinness of the margin, 

 abrupt elevation of the centre, and reticulated structure of the 

 lateral masses are especially characteristic of both, although the 

 abrupt elevation may not always be present in either. The 



