100 Mr. H.J. Carter on the Structure of the Shell of Alveolina. 



cross the grooves, which, like those on the surface of a melon, 

 divide the segments and offering a triangular space are filled up 

 by corresponding portions of the shell in the form of ribs (fig.l a). 

 Through each rib also there is a triangular canal (fig. 4 b & 5 a), 

 which extends to either extremity of the fossil, where again it 

 may have communicated with the exterior by a foramen or um- 

 bilical hole apparently in the latter (fig. 2 a). Behind and also 

 internal to the triangular canal there appears to have been 

 another longitudinal channel of communication, formed by a 

 deficiency in the partitions of the canals at this part (fig. 4 c & 

 5 b). Although the partitions generally appear to have been 

 continuous under the ribs, yet in many instances they seem to 

 alternate, or nearly so, with the interspaces or canals in the ad- 

 joining segments. Whether there was any communication be- 

 tween the canals and the chambers (fig. 3 b) future investigation 

 must determine ; at present there appears to be no other outlet 

 for them ; and if this be the case with Alveolina, it may also be 

 the case in many other forms of Foraminifera. Of what use 

 then can the chambers be ? 



Although I have mentioned holes, channels, canals, and cavi- 

 ties in this fossil, yet in reality there is no such thing ; but from 

 their having been filled with transparent calc-spar they are 

 easily recognized, in contradistinction to the white amorphous 

 carbonate of lime which has replaced the shell itself. 



The specimens of Alveolina in which I first noticed the posi- 

 tion of this canaliferous structure were, as before stated, pre- 

 sented to the Asiatic Society by Dr. Leith, who broke off the 

 portions of limestone containing them from rocks in the Bolan 

 Pass, between the towns of Dadur and Quetta. 



They are associated, as in Scinde and Arabia, with papyra- 

 ceous Orbitolites (Cyclolina, D'Orbig.), and the white compact 

 limestone containing them is that which in this part of the world 

 is generally called " nummulitic ?' but in only one or two in- 

 stances have I seen Alveolina mixed with Nummulites, and then 

 only very sparsely scattered throughout the mass, though it is 

 quite possible that the opposite may be the case, for they must 

 be close together. The easiness, however, of mistaking Orbi- 

 tolites for Nummulites, in the rock, and the occurrence of Cyclo- 

 lina and Alveolina together in great abundance in the white com- 

 pact limestone of the south-east coast of Arabia (which I take to 

 be the same as that of Scinde and the Bolan Pass) far below the 

 position of the Nummulites, together with the existence of these 

 two fossils in the Chalk of Europe (D'Orbigny), induces me to 

 think, that much of the white limestone in the East is called 

 " nummulitic," which will hereafter be found to be an equivalent 

 of the Chalk. 



