GENERA CIIRYSALIDINA AND CUNEOLINA. 193 



paralleled by those which occur in the Miocene and Pliocene deposits of Vienna and 

 Palermo. 



Genus IX. — Chrysalidina (Plate XII, fig. 16). 



324. Hisfori/. — This genus was created by D'Orbigny in 1846 (lxxu), for the reception 

 of a peculiar modification of the Textularian type, which, so far as is at present known, is not 

 connected with it by any intermediate gradations. 



325. Ed-tenal Characters and Infernal Structure. — The name of this genus expresses the 

 pupoid form of its shell, which results from the tri-serial arrangement of its chambers, and 

 from the peculiar oblique mode in which they are set one upon another, as shown in Plate XII, 

 fig. 1 6. The essential difference of this type, however, from JWttdaria appears to consist in 

 the mode of communication of the chambers ; for the apertural passages by which each cham- 

 ber of one series communicates with the alternating chambers of the adjacent series in the tri- 

 serial Textdarice seems to be here wanting ; being replaced by a set of very large " orbuline" 

 pores, which are dispersed over nearly the whole anterior wall of the last chamber. These 

 pores, which have fully twice the diameter of the ordinary pores of the shell, are sometimes 

 continued externally into short tubes, which project fully the lengtli of their own diameter 

 from the convex septal plane. From the mode in which the older segments are partially 

 overlapped by the newer, the communication between each chamber and that which succeeds 

 it in the spiral alternation will be maintained by those pores which pass through that part of 

 the anterior wall which forms the posterior wall of the next chamber. — The most characteristic 

 specimens of this type present themselves only in the Lower Chalk, near the mouth of the 

 river Charente ; but small dimorphous examples of it are met with in the Indian Ocean and 

 Panama Bay, which, commencing tri-serially, soon take on a uni-serial mode of growth, 

 continuing to maintain their triangular form to the end, and progressively increasing the 

 size of their segments, which is contrary to the rule of uni-serial growth in other bi- or tri serial 

 types. 



Genus X. — Cuneolina (Plate XII, fig. 17). 



326. History. — The first and only original account of this curious type is that which was 

 given by M. D'Orbigny (lxxi) in 1839, on the basis of specimens found only (hke those of 

 the preceding type) in the Lower Chalk, near the mouth of the Charente. 



327. External Characters and Internal Structure. — The form of this shell (Plate XII, fig. 1 7) 

 is that of an almost equilateral triangle with a curved base ; and its two flattened surfaces are 

 marked by a succession of parallel curved septal bands, apparently indicating a uni-serial suc- 

 cession of chambers whose breadth bears an unusually large proportion to the distance 

 between the septa. When the shell is viewed edgeways, however, it is seen that the two 

 external surfaces belong to two different series of chambers, whose internal surfaces are closely 

 applied to each other ; and it is further to be noticed that the chambers of the two series 



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