164 Mr. H.J. Carter on Fossil Foraminifera in Scinde, 



which is the case. D'Orbigny's grand distinction, thei-efore, of 

 the spire not being embracing in Assilina, would seem to be more 

 apparent than real, and although sufficient for common purposes, 

 yet, if we add to it the absence of chambers above and below the 

 central plane, we shall not only have a real, but a more evident 

 distinguishing sign for Assilina than the one just mentioned. 



Second, as regards the division of Nummulina into subgenera. 

 It appears to me that this may be advantageously done by sepa- 

 rating those in which the septa extend from the circumference 

 to the centre in more or less continued sinuous lines (Plate VII. 

 figs. 11 & 15), from those in which these lines are so branched and 

 inosculate as to present a densely reticulated structure (fig. 21). 



These difi'erences have already been alluded to by Dr. Cai-- 

 penter {loc. cit.). 



In the latter subgenus would then come Nummularia acuta ?, 

 Sowerby, which borders close upon Orbitoides, from possessing 

 this reticulated structure on the surface, a comparatively less 

 development of the spire and chambers, a tendency to an abrupt 

 prominence in the centre, and an expanded thin margin. 



From N. acuta we should then pass on to Lycophris disjiansus, 

 Sowerby, where the spire is still more incomplete, and then to 

 Orbitoides MantelU, or Orbitolites Mantelli (for we shall see here- 

 after that we must make this an Orbitolite), where the spire is 

 entirely lost. 



In the last two genera I have been at much pains to ascertain 

 if the rows of chambers in the central plane are arranged spirally 

 or concentrically, and I think that I have been as successful, as, 

 under the circumstances, we can expect to be. 



For some time I was unwillingly obliged to yield to the opi- 

 nion of D'Orbigny, that the rows of chambers commenced con- 

 centrically, for having taken adult specimens of Lycophris dis- 

 pansus and Orbitoides Mantelli for sections, I found the centre 

 in each species invariably filled with calc-spar, which apparently 

 was surrounded by circles of chambers at its circumference, that 

 is, where the latter began to appear. Hence I had given up 

 almost all hope of being able to determine this satisfactorily, 

 when I conceived that the origin of this structureless centre 

 might be owing to a decay of the central chambers only in the 

 adult animals and its subsequent filling with calc-spar during 

 fossilization ; and, that if I took very young individuals, I might 

 obtain what I wanted. Accordingly I made sections of spe- 

 cimens not larger than the 24th part of an inch in diameter, and 

 found just what I had expected, viz. the centre in its natural 

 state, that is, filled with chambers to the central point. 



I will now shortly describe the central planes in both these 

 species, reserving a more particular description of them until 

 we come to the descriptions of the species themselves. 



