100 W. B, CARPENTER ON THE STRUCTURE OF ORBITOLITES, 



# B w 



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TO 



s 



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In 1 





igp! 



in. „-? mp 



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Fig. 11. 



Diagrammatic representation of the 

 transition from the " simple " to the " com- 

 plex " plan of growth, as shown in vertical 

 section, from the primordial and circum- 

 ambient chambers (c p cf) of the centre, 

 to the margin, whose pores are shown at 

 mp. The chambers m, m 1 , m 2 , m 3 , rrfi, are 

 all formed upon the simple type (as in 

 Fig. 8, 4 ) ; and show at ac, ac, the cross 

 sections of the annular canals, which con- 

 nect all the chamberlets of one ring, and 

 at r, r, r, the radial passages connecting 

 the successive annuli. The chambers 

 d, d l , d 2 , are formed upon the duplex 

 type ; the annular cannls ac, ac, being 

 single, but the radial passages r being 

 double. The chambers e, e 1 , show two 

 annular canals ac, ac', between which is 

 interposed a columnar chamberlet, con- 

 tinuous with the two superficial chamber- 

 lets s s. In the chambers f,/ 1 ,/ 2 ,/*, 

 to the margin, which are all formed on 

 the fully-developed complex type, the 

 upper and under superficial chamberlets 

 s s, s' S', are completely cut off from the 

 intermediate columnar portion, and, by a 

 shifting of their position, each is made to 

 communicate with two annular canals. 



