246 FAMILY NUMMULINIDA. 



honeycombed with minute depressions, which do not extend, liowever, veiy far into their 

 thickness ; whilst in other cases each lobe is divided for a great part of its length into two, 

 three, or even four, narrow bands, connected with each other at intervals, so that the whole 

 lobe has the character of a network, the meshes of which are occupied by the tubercles or 

 elevated lines of shell-substance (Plate XIII, fig. 29). These tubercles or lines, rising through 

 the whole thickness of the alar lobes, join themselves on, like the septa between the lobes 

 themselves, to the spiral lamina; and, as they consist of non-tubular shell-substance, there are 

 no tubuli to pass on into the portion of the spiral lamina which overlies them ; and thus their 

 position is marked on its surface by clear lines, usually more or less interrupted, which inter- 

 vene between those that mark the position of the subjacent septa (fig. 22). The alar lobes 

 often communicate with those adjacent to them by connecting bands of their own ; and it 

 sometimes happens, especially in specimens in which these lobes are most broken up, that 

 these communications are almost as numerous as those uniting the different bands of the same 

 lobe ; so that the portion of the sarcode body covering the lateral surface of the shell forms 

 one continuous network, in which the division into alar lobes is scarcely distinguishable. 

 This varietal modification is of peculiar interest, as representing in this type the still more re- 

 markable modification of the alar prolongations which we shall find to be characteristic of 

 certain forms of Nummulina (^ 462). 



427. The various forms of AmpMstefjina which have been ranked as distinct species differ 

 from each other only in characters which our extended study of this group has led us to 

 regard as non-essential ;• — such as the degree of convexity of the shell in proportion to its 

 diameter; the amount of inequality between its two lateral halves; the amount and kind of 

 exogenous deposit on its surface ; the number of chambers in each whorl, and the proportional 

 distance between their septa ; the degree of backward curvature of the septa of the marginal 

 portion of the convolution ; and the mode in which the astral lobes of the under side are 

 intercalated between the marginal segments. The differences in all these particulars which 

 may be presented by individual specimens, arc found, when large numbers are examined, to be 

 so gradational, that no definite lines of division can be drawn between them. In point 

 of size, there would seem at first sight to be a marked distinction between the recent 

 and the fossil examples of this genus ; for whilst the diameter of the former does not 

 ordinarily exceed 1-1 4th of an inch, and is often not more than l-20th, that of the latter some- 

 times attains l-7th of an inch. This difference, however, no more constitutes a valid specific 

 distinction, than do any of the preceding ; for I have recent specimens from the Philippine 

 seas, which attain a diameter of 1-lOth of an inch, and which are yet unquestionably of the 

 same type with the ordinary examples of not half their diameter. 



428. Affiniiies. — From a comparison of the preceding description with the account of the 

 Rotaline type given in the preceding chapters, it will be evident in what particulars Ampliisfe- 

 fji'iia presents the characteristic features of that type. The turbinoid spire, the consequent 

 inequality of the upper and under sides, the limitation of the aperture to the under side, and 

 the obliquity of the septal plane, are all Rotahne peculiarities ; the singleness of the septal 

 lamella: is a most important additional hnk of affinity to that group, and so also is the distinct- 

 ness of the " astral lobes," which specially links An/ji/iisfc^ina to Itotalia (% 371). All these 



