19S FAMILY GLOBIGERINIDA. 



chambers of the two alternating series, some of which may be made to appear by the obliquity 

 of the spire as if they were small and intercalated (ex, Fig. 141). The earlier turns of the 

 spire are in general completely enclosed by the later ; but sometimes the axis of the spire is 

 so oblique, that much more of the earlier portion is seen on one side than on the other. The 

 septal plan is flat and oblique, facing alternately towards opposite sides ; and the aperture is a 

 curved slit, commencing at the junction of the septal plane with the preceding convolution, and 

 extending about half way across the septal plane, usually in a direction parallel to its lower 

 edge (ex, Figs. 141, 142), but sometimes becoming crozier-shaped, as in some of the uncoiled 

 varieties, or even doubling abruptly back upon itself, so as to form a kind of valve or tongue, 

 as in the C. crn.-im of D'Orbigny (lxxiii). The general form of the shell is subject to 

 variations similar to those which we have seen to present themselves in BuUmhia and 

 Te.riidariri ; the segments being ventricose in some instances, and flattened in others ; and the 

 margin being obtuse and rounded in some instances, thin and carinate in others. — A much 

 greater departure from the typical shape is presented by the Ehrenhergina of Reuss (lxxxvii), 

 which is a Cassidulina in every essential particular, but has the later portion of its spire uncoiled, 

 showing very clearly the bi-serial interdigitate arrangement of the segments (Plate XII, fig. 23). 

 After the evidence which has been given in such genera as Peneroplis and Xodosaria of the 

 little reliance to be placed on the direction of the axis of growth as a differential character, 

 it is impossible to regard Elirenheryina as anything but a varietal form of Cassididbia. 



339. Affiniiies. — This genus may be regarded as the culminating form of the Textularian 

 series, which nowhere graduates into any type of a character more elevated than its own. In 

 the finely porous texture of its shell and its slit-like aperture, it is obviously more allied to 

 BuUmhifi than to Tcxtularia ; whilst, in the bi-serial interdigitate arrangement of its chambers, 

 it is more closely akin to Textularia than to the typical Bidiniina. 



340. Geographical and Geological Distrihition. — Like the preceding genus, Cassidulina seems 

 to have a world-wide distribution in shallow, moderately deep, or even very deep waters ; being 

 found at depths of from thirty to seventy fathoms on the west coast of Greenland, also off" 

 Norway, Shetland, and various parts of the British and Irish coasts ; whilst the larger and 

 thicker forms with smooth shining walls occur in tropical seas at depths of from thirty to 

 one thousand fathoms. — This genus presents itself in the Tertiaries of New Zealand (Eocene?), 

 Menna, Sienna, and Palermo ; but it has not been recognised in any older formations. 



SUB-FAMILY ROTALIN^. 



341. The assemblage of forms which constitute in our view the Eofalinc sul>family or 

 series is the most numerous and the most varied that is presented by any corresponding 

 group ; and as a consequence of that variety, the relations of these forms to each other have 

 been singularly misconceived. Misled by superficial differences masking real resemblances, 

 M. D'Orbigny created several genera for their reception, which in our view have no title 

 whatever to that rank. On the other hand, his ignorance or his want of appreciation of 

 differences of far greater importance, led him to associate in the same genera types which 



