Mr. II. J. Carter on the Structure of the Shell of Alveolina. 99 



VIII. — On the true position of the Canaliferous Structure in the 

 Shell of Fossil Alveolina [D'Orbigny). By H. J. Carter, Esq., 

 Assistant Surgeon, Bombay Establishment. 



[With a Plate.] 



In the description of Alveolina melo, given at p. 170. vol. xi. of 

 this Journal, I have stated, that the " transverse parallel ridges " 

 seen on the outside of the fossil correspond to the "divisions," 

 or rather partitions, in the interior of the chambers. D'Orbigny 

 also has stated, that the chambers in Alveolina are " divided 

 into a great number of capillary cavities by partitions longitudinal 

 to the enroulement" (Foss. Foram. du Bassin Tert. de Vienne, 

 p. 143) ; and so most people would think, jndging from the ex- 

 ternal appearance of the shell ; but when the interior is examined 

 by a section made through the longitudinal axis (PI. III. B. fig. 3), 

 then these divisions and this canaliferous or capillary structure 

 are seen to be confined to the external walls of the chambers, and 

 to be completely excluded from their interior. 



The oversight has arisen from the last whorls of the shell 

 being in such close approximation with each other, that there 

 seems in most instances to be no space for the chambers left be- 

 tween them, and hence the appearance of the openings of the 

 capillary canals along the free border of the last-formed segment 

 could hardly be inferred to lead to anything but the chambers 

 themselves; while the intervals between the transverse ridges, 

 too, would also lead to the inference that the latter were so 

 many partitions dividing the chambers into as many cavities 

 arranged longitudinally with respect to the direction or enroule- 

 ment of the shell (figs. 3, 4). 



It was only a few weeks since, however (although I had fre- 

 quently seen and even sketched it), that I recognized the true 

 position of this canaliferous structure, when cursorily examining 

 some specimens of Alveolina which had been presented to the 

 Asiatic Society of Bombay by Dr. Leith, and I was instantly 

 struck with its analogy in position and nature to the reticular 

 canaliferous structure in the spicular or marginal cord of Oper- 

 culina Arabica (PI. IV. vol. x.). 



The canals are about l-400th of an inch square, and the 

 partitions which separate them about a third of this breadth 

 (fig. 3 b), sometimes much thinner. They appear to open b}^ a 

 single row of apertures in the free edge of the last-formed seg- 

 ment of the shell, and from thence to be continued into the very 

 centre, following the spire and being confined to the walls of the 

 shell the whole way. On their course they dip inwards as they 



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