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posed lamellae. The chamber is covered-in above and below by 

 successive layers of a minutely -tubular and peculiarly-compact shell- 

 substance, resembling dentine in its general aspect ; certain parts of 

 this, however, are non-tubular, and form cones, of which the bases 

 appear on the surface as minute rounded tubercles. The adjacent 

 chambers of the same row do not seem to communicate with each 

 other ; but each chamber communicates with two chambers of the 

 previously- formed row, and, in like mariner, with two of the subse- 

 quently-formed row, by narrow passages, the number and position of 

 which are by no means constant. These passages seem to afford the 

 principal means whereby the segments of the sarcode-body occupy- 

 ing the inner chambers, can be nourished from the exterior ; but it 

 is by no means impossible that the tubuli of the shelly laminae that 

 invest the chambers above and below, may also be subservient to this 

 purpose, since, however numerous may be the laminae, the tubuli 

 are continued through them all from the cavity of the chamber to 

 the external surface. 



The almost entire separation of the segments of the sarcode-body 

 in these two genera, the investment of each of them with its own 

 proper envelope of shell, the minutely-tubular structure and firm 

 consistence of the shell-substance, and the interposition of the inter- 

 mediate skeleton with its canal-system, are features that place them 

 in such marked contrast with Orbitolites and Orbiculina, that, not- 

 withstanding their conformity to those two genera in their respective 

 plans of growth, it is scarcely possible for them to be more widely 

 removed in everything that relates to their respective physiological 

 conditions. 



From a comparison of the five genera whose structure has been 

 thus elucidated, the author deduces the conclusion that, in this 

 class, external form, which depends exclusively on plan of growth, 

 affords no clue whatever to internal structure ; and that the latter 

 alone, as the exponent of the physiological condition of the animal, 

 can afford the basis of a natural classification. 



