150 CARBONIFEROUS AND PERMIAN FORAMINIFERA. 



The canal-system of the septa and marginal cord may be traced here and there, 

 though only imperfectly. The transverse section (fig. 10) gives distinct evidence of the 

 existence of the marginal cord, but the details of the structure are obliterated ; and in 

 the more highly magnified drawing (fig. 11) indications are not wanting of canals 

 traversing the septa as well as the supplementary skeleton. 



Such is a detailed account, as far as can be furnished from the materials available, of 

 the finer specimens of this Carboniferous Nuramulite ; and in the absence of larger 

 individuals or of fragments indicating their existence, they may fairly be supposed to be 

 adult and fully developed examples of the species. But, in addition to these, a number 

 of smaller individuals have been found apparently belonging to the same form, though 

 neither so uniform in external appearance nor so unmistakably Nummuline in character. 

 One or two are somewhat explanate in their mode of growth, and if mature may pertain 

 to an ' Assiline ' variety. Others, smaller still, not much more than a hundredth of an 

 inch in diameter, are unsymmetrical, the convexity of the two faces being unequal and 

 irregular. They probably represent either one of the early stages of the organism or 

 perhaps an arrested condition of growth. Their precise relation to the better developed 

 form must be left for future determination, in the lack of sufficient specimens to work the 

 question fully out. 



Referring to D'Archiac and Haime's Monograph, 1 the figures most closely resembling 

 N. pristina are those of N. variolaria, Sowerby, which represent a Nummulite of 

 somewhat larger dimensions, but remarkably similar in general external characters and 

 septation. Thus the nearest allies, zoologically speaking, of the Carboniferous form are 

 the small thick members of the "radiate" group, regarded by Profs. Parker and 

 Jones as the western modifications of N. planulata? N. variolaria especially is a poor 

 and variable form whose descent may be easily traced. 



It is not a little singular that in the Carboniferous precursor of the Nummulitic 

 group we should have an organism so exactly corresponding in minutest features with 

 its most modern representatives. This cannot be a mere coincidence. Is it not rather 

 a curious exemplification of persistence of essential characters through innumerable 

 ages, whilst modifications of the original, forming collateral " species," have, under 

 favourable circumstances, exhibited an extraordinary development in size and complexity 

 of structure and a corresponding increase in geological importance ? Then, as external 

 conditions have become less favourable, little by little, the type has reverted to its 

 primitive state, gradually dwindling in size, and losing by degrees those minor characters 

 which were the easily recognised evidence of higher organization, and in its later history 

 suggesting the lingering stages which precede complete extinction. 



Distribution. I can add nothing to what was stated in the paper containing the 



1 'Descr. des Anim. foss. du groupe Nummulitique de 1'Inde,' p. 146, pi. ix, figs. 13, a g. 

 " See Messrs. Parker and Jones on the nomenclature of the genus, ' Ann. and Mag. Nat. Hist.,' 

 3 ser., vol. viii, p. 231. 



