THE FORAM1NIFERA 



57 



but in other genera it forms extensive deposits in the interior of 

 the septa, and on the surface of the tesf. It attains a great 

 development in Calcarina. 1 



Where the canalicular skeleton comes in contact with that of 

 the chamber walls, the two merge insensibly into one another ; the 

 only distinction between them is that one is penetrated by the 

 branches of the canal system, the other by radiating pores leading 

 direct from the chambers of the test. 



Some confusion has arisen in the use of the terms intermediate or 

 supplemental skeleton, and proper chamber wall. In the Introduction to 

 the Study of the Foraminifera (p. 50) Carpenter says that the "intermediate 

 or supplemental skeleton " is " formed by secondary or exogenous deposit " ; 

 and further, that wherever developed to any considerable extent, " it is 

 traversed by the canal system." The statement that the supplemental 

 skeleton is formed by a secondary or exogenous deposit appears unfortunate, 

 for the walls of the chambers of all the perforate calcareous forms are at 

 first exceedingly thin, and they increase in thickness by the deposition of 

 shell substance on their outer surface, so that the greater part of the 

 shell in all may be said to be secondary and exogenous. The part of the 

 shell first formed is in most, if not all, cases quite indistinguishable from 

 that which is added later. 



The second character of the supplemental skeleton given by Carpenter, 

 that it is traversed by the canal system, does, however, touch on a real 

 distinction. 



Biitschli (6, pp. 26-27) calls attention to the fact that a difference 

 between a primary shell layer (Carpenter's "proper wall") and a 

 secondary mass is often indistinguish- 

 able ; but he proposes to use the 

 latter term for the outer layer of 

 the shell, whether unperforated, 

 perforated by radial pores, or by 

 branches of the canal system. 



It appears to be more advan- 

 tageous to distinguish the skeleton 

 developed in relation with the canal 

 system from that of the chamber 

 wall, and as confusion is attached 

 to the name supplemental skeleton, 

 the term canalicular skeleton is 

 used in this article for the former. 



Repair. The power of re- 

 pairing injuries is very great, 

 and indeed a fragment may, 

 in some cases, give rise to a 

 new individual. This is well 

 seen in the specimen of Orbitolites tenuissima shown in Fig. 4, 



1 Cp. Carpenter, 8, p. 216. 



FIG. 4. 



Specimen of Orbitolites tenuissima in which 

 a fragment of a test has given rise to a new 

 disc. (From Carpenter, 9, Plate I. Fig. 7.) 



