GENUS NUMMULINA. 267 



and 4^ inches ; a considerable proportion of the reputed species ranging between half an inch 

 and'an inch. This type is consequently the most gigantic in its dimensions of all Foraminifera ; 

 its largest forms being only approached by Tliioporiis, Cychclypcm, and Alvcolina, whilst its ordi- 

 nary size is equalled by that of none save PatdUna, Orbitoides, and OrhiloUte^. The fossilized 

 specimens which afford us the most abundant means of studying this type, very seldom present 

 what was probably their original surface quite unaltered, having nearly all been subjected 

 to more or less of abrasion or decomposition ; but in those which seem to have been least 

 affected by such agencies, the surface may be either entirely smooth, without any indication 

 whatever of the spiral convolution concealed within, or it may exhibit various inequalities 

 which are related to the peculiarities of internal structure to be presently described. In the 

 typical Nummulites, the last turn of the spire not only completely embraces but entirely 

 conceals all those which preceded it ; but in the group which has been formed by some into 

 the separate genus Jssilina, ranked by others as a sub-genus of Nummulites, and merely 

 distinguished by MM. D'Archiac and Haime as the exj}Ianate form, the earlier whorls remain 

 more or less visible, in consequence of cither not being invested at all by the later, or being 

 so invested that (as in Operadind) their spiral and septal partitions are not concealed. This 

 feature, however, is by no means peculiar to the explanate group ; since it presents itself 

 occasionally in specimens which are referred by other characters to a different position ; and 

 this kind of variation will not be surprising to such as have learned to appreciate at their true 

 value the corresponding variations of Operculina (% 441). In the type of this genus which 

 has come down to the present epoch, the N. plannlda, of which the N. radiata of Fichtel 

 and Moll is a varietal form, we find the centre of each lateral surface occupied by a " boss" of 

 transparent shell-substance, exactly resembling that which has been described as occurring 

 in Ampldstegina (% 421), and formed like it, by the filling-up with exogenous deposit of the 

 umbilical hollow left by the stopping-short of the alar prolongations, which, in the later 

 whorls, do not by any means extend to the centre. 



457. The lateral surfaces, again, are often marked by punctations, which are sometimes 

 depressed, but are more commonly elevated into rounded tubercles. The presence of these 

 in unusual abundance and jjrominence has been held by MM. D'Archiac and Haime to cha- 

 racterise their group ol punctidata ; but as I am nov^- fully satisfied that these punctations 

 (whether elevations or depressions) only mark, as in Operculina, the spots in which the 

 ordinary canaliculated shell-substance is replaced by the solid or non-tubular, and that they 

 are not (as supposed by those and other observers) the indications of canals filled-up during 

 fossilization, I cannot attach any essential importance to their larger or smaller size, or to their 

 greater or less abundance, feeling confident that this character must be subject to the same 

 kind of variation in Nuramulito that we have seen it to present in OjjnrcuHna^- When the 

 surface has been worn by abrasion, moreovei', the non-tubular portions of the sliell, being 



* On tliis point, I find myself supported by tlie careful observations of Mr. Carter, who re- 

 marks (xxiii a, p. 371) : — "The presence of the puncta, again, or their absence, their attachment to the 

 septal lines, or their separation from them, or the existence of both in the same specimen, or, indeed, 

 the absence of septal lines altogether, and the presence of an abundance of pinicta, may exist, re- 

 spectively, in the dift'erent forms of the globose Nummulite, N. inrforalu, which abounds in the valley 



