CARPENTER ON FORAMINIFERA. 193 



of two distinct laminae, which diverge from each other where they give 

 passage to the canal system, and which are often further separated by 

 the intervention of a portion of the intermediate skeleton. The pas- 

 sages of communication between the chambers are so narrow, that seg- 

 ments of the body are much more isolated from each other than they 

 are in the type already described ; and the proper walls of the chambers 

 seem, as it were, to be moulded upon the segments, instead of merely 

 filling- up the interspaces, between them, as they there do. This filling 

 up, in fact, is the office of the intermediate skeleton, which gives 

 a solidity to the whole aggregation that it would otherwise want ; and 

 special provision, as we have seen, is made in the canal system for its 

 nutrition. Altogether this type is the one in which the Foraniiniferous 

 structure attains its highest development, and which is most completely 

 differentiated from every other. And the morphological variations it is 

 known to undergo seem to me fully to justify the inference that such 

 further variations as have been shown to occur in the Orbiculine typo 

 might be regarded as the probable source of the divergence from some 

 common ancestral stock of the several forms whose intimate relationship 

 I have demonstrated. The analogy of that type would suggest Iletero- 

 stegina as presenting the nearest existing approximation to such a com- 

 mon original ; and the stages of differentiation may be thus expressed : — 



HETEROSTEGIXE TYPE, 



Diverging into 



QPERCTJLINA. HeTEROSTEGINA. 



Amphistegina, jNTuniniulites, Operculina. Heterostegina, Cycoclypeus. 



From my imperfect acquaintance with Fusirfina, I do not feel justified 

 in expressing its exact relationship to either of the forms included in this 

 scheme; and, for the same reason, I abstain from connecting Orbitoides 

 with Cyclochjpeus, to which it has some features of close relationship.^ 



After this detailed examination of the general relations of the 

 principal modifications of two of the most strongly-marked types to be 

 found in the whole group of Foraminifera, it seems needless for me to 

 do more with respect to the other forms whose structure I have inves- 

 tigated, than to inquire how far the peculiar characters by which they 

 are respectively distinguished show evidence of a like variability. Thus 

 I have shown (4th series) that Calcarina is essentially distinguished from 

 Rotalia by the extraordinary development of the intermediate or supple- 



* The figure given by Prof. Ehrenberg, in his remarkable memoir already referred 

 to, " Ueber den Griinsand und seine Erlauterung des organischen Lebens," Plate IV., 

 fig. 8, and by him designated as the internal cast of Orbitoides javaniens, will be seen 

 on comparison to present a most remarkable correspondence with figs. 10, 11, 12, of 

 Plate XXIX., illustrating my description of Cycloclypeus. 

 VOL. I. N. U. R. 2 C 



