10 CARBONIFEROUS AND PERMIAN FORAMINIFERA. 



Family GLOBIGERINIDA. 



Family NUMMULINIDA. 



B. WlTH EXCEEDINGLY POROUS, CAL- 



CAREOUS SHELLS. 



1. Hotalidea. 



C. WlTH CALCAREOUS SHELLS, TRA- 



VERSED BY A RAMIFIED CANAL- 

 SYSTEM. 



1. Polystomellidea. 



2. Nummulitidea. 



Note. Professor A. E. von Reuss's classification is taken from the " Postscript" to his paper 

 ' Entwurf einer systematischen Zusammenstellung der Foraminiferen,' not from the body of the memoir. 

 The primary division into " Foraminifera Monomera" and " Foraminifera Polymera," originally laid 

 down, is abandoned in the postscript. His group Gromidea, corresponding with the GROMIDA of the 

 English observers, is omitted entirely in the revised scheme. In the proximate correlation of the two classi- 

 fications, given above, the principal discrepancy occurs in the sub-order Perforata. The LAGENIDA 

 and GLOBIGEKINIDA together are almost exactly coextensive with Von Reuss's two sections B, ^4 and #,but 

 the (I) Spirillinidea, (2) Ovulitidea, (7) Textilaridea, and (8) Cassidulinidea, together with one or two 

 genera from other groups, find place amongst the GLOBIGEKINIDA of the British classification, and the 

 family LAGENIDA is correspondingly reduced in extent. The family NUMMULINIDA corresponds exactly 

 with Von Reuss's section B, C. 



In his latest memoir ('Das Elbthalgebirge in Sachsen,' 2ter Theil, 1874) Professor Reuss again some- 

 what modified his classification, making three primary groups of equal zoological value, and reversing the 

 order originally adopted, thus.-- A. Kalkschalige Foraminiferen, B. Porenlose Foraminiferen, 

 C. Kieselschalige Foraminiferen; but the general features of the classification are otherwise unchanged. 



It will be seen at a glance that the " families " of the German arrangement are much 

 smaller and more numerous than those adopted by the English naturalists, but this is 

 counterbalanced by the more comprehensive " generic types " of the latter. The essential 

 difference, not only between the two systems of classification, but in the entire methods 

 of study and nomenclature, lies in the different values of their respective " genera " and 

 " species." A purely artificial classification is ill adapted to the conditions presented by 

 a class of organisms like the Foraminifera, largely made up of groups of which the 

 modifications run in parallel lines. This " isomorphism," demonstrated chiefly by the 

 labours of Messrs. Parker and Jones, whilst it is the source of most of the difficulties the 

 systematist has to contend with, is at the same time the key to the natural history of the 

 order as at present accepted. It exists not merely between a single series, in one of the 

 larger divisions, and a single series in another, but often amongst several series even of the 

 same family. It not unfrequently happens that a member of one group presents a greater 

 similarity to its isomorph in another group with which it has no relationship, than it does 

 to any other member of its own. Take a familiar illustration suppose the fingers of the 



