6^e/jws Orbitoides ofd^Orhigny. 443 



India; Carter (reprint), Bombay, 1857, p. 587). The cells 

 of which Orhitolites marginalis is composed are spheroidal and 

 so arranged respectively in the interstices of obliquely inter- 

 crossing lines which radiate centrifugally from the centre to 

 the circumference in opposite directions as to present the 

 same " engine-turned " appearance as that of the central 

 plane of Nummulites MantelU ; and not being accompanied 

 by the conical " columns " of opaque shelly substance, 

 incipient or otherwise, they thus altogether present pre- 

 cisely the same appearance as that of the central plane of 

 Nummulites Mantelli. Hence by the evolutionary develop- 

 ment of the collateral crusts of Nummulites Mantelli it so 

 becomes allied to Orhitolites marginalis that I have been led 

 to adopt the name of Orhitolites Mantelli for the former in 

 contradistinction to that of "Orhitoides " in 0. pap^/racea and 

 its like, which, on the other hand, all together seem to be 

 equally based upon another type of Foraminifera, viz. Cgclo- 

 clyi^eus. 



Thus Cycloclyj)eus, Carp. (' Introduction,' pi. xix.), con- 

 sists horizontally of a thin discoid test, which is composed of 

 a number of rows of rectangular chambers that radiate cen- 

 trifugally from the centre, in the angles of which chambers 

 are incipient conical pillars of opaque white shelly substance 

 (" cones of non-tubular substance," Carp., see fig. 5, op. et 

 he. cit.), whose obtuse ends project beyond the surface in the 

 form of little knobs, so as to give it a granular appearance, 

 whereby the form is simply that of the central plane of Orhi- 

 toides papyracea and its like. Thus by the evolutionary 

 development of the collateral crusts of the latter it so be- 

 comes allied to the former that Orhitoides papyracea (following 

 the same reasoning) must be regarded as much a derivative 

 from Cycloclypeus as Orhitolites Mantelli is from Orhitolites 

 marginalis ; and hence the difference in the structure of 

 these fossils to which I have alluded. 



The same with Nummulites^ which, mutatis mutandis^ 

 appears to be an evolutionary development of Operculina. 



It is evident that Giimbel must have seen this or he would 

 not have proposed a subgenus of Orhitoides, d'Orb., viz. 

 '"'■Lepidocyclina^'' for species of the type of Orhitolites Man- 

 telli= Orhitoides Mantelli^ d^Orb. ((iiimbel, op. cit. p. 139, 

 separate copy). 



All this I pointed out in 1861 (' Annals,' vol. viii. pi. xvi.) ; 

 the plate then given is entirely devoted to parallel columns of 

 structural illustrations, in order that the facts I have stated 

 might be directly realized. Whether or not this has had the 

 desired effect I cannot say, but at all events in de Lapparent's 



