FORAMINIFERA. 1 23 



double chamber-walls, supplemental skeleton, and a system of canals. 

 Ex. — Rotalia, Discorbiiia^ Carpenterid^ Calcarina, Tinoporus. 



Family 10. NUMMULlNlDiE. — Test calcareous and finely tubulated ; 

 typically free, polythalamous, and symmetrically spiral. Usually a " sup- 

 plemental skeleton " and canal-system. Ex. — Nummulina, Polystomella, 

 Fits7ili?m, Nonionina. 



In connection with the general subject of the classification of the 

 Foraminifera, the following remarks by Dr Brady may advantageously 

 be quoted ; since they not only have a most important bearing upon 

 the special point in question, but forcibly express the principles 

 which should guide the philosophic naturalist in his systematic treat- 

 ment of all such variable forms of life : "A purely artificial classifi- 

 cation is ill adapted to the conditions presented by a class of organ- 

 isms like the Foraminifera, largely made up of groups of which the 

 modifications run in parallel lines. This 'isomorphism,' demon- 

 strated chiefly by the labours of Messrs Parker and Jones, whilst it 

 is the source of most of the difficulties the systematist has to con- 

 tend 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, with 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 rela- 

 tionship, than it does to any other member of its own group. Take 

 a familiar illustration — suppose the fingers of the two hands to repre- 

 sent the modifications ('species') of two such parallel types of Fora- 

 minifera : the thumb of one hand resembles more closely the thumb 

 of the other hand than it does any other of the fingers on its own. 

 In other words, the extreme member of one series bears greater 

 similarity to its isomorph in the other series than it does to its own 

 nearer relations, and so on through the remaining members of the 

 respective groups. Under conditions like these, artificial subdivision, 

 based upon minor morphological characters, is certain to infringe 

 the order of nature, owing to its tendency in some cases to separate 

 forms closely allied, and in others to place together such as have no 

 natural affinity." 



The principal fossil groups of Foraminifera require a brief con- 

 sideration, but in the short summary of these which follows — as in 

 the case of similar summaries which will subsequently be given — it 

 will be understood that nothing further is proposed than to select for 

 notice and characterisation those leading types of each great group of 

 fossils which may seem to demand mention on the ground of their 

 being common, or in other respects, geologically or zoologically, of 

 peculiar importance. For anything like a complete list of the known 

 structural types of each group, or the characters of all the recorded 



