216 FAMILY GLOBIGERINIDA. 



ments that form each new annulus of chambers, since the chambers of one annulus have no 

 direct communication with those of the annulus which preceded it. In this respect, there- 

 fore, we have a curious analogy to Dactyhpora, in which, however, the independence of the 

 segments is greater, no communication existing between even those of the same annulus 

 (f 190). 



376. The mode in which the spiral growth is exchanged for the concentric seems to be 

 essentially the same with that in which it is accomplished in PlanorbuJum (f 358) ; the spire 

 first becoming excentric by the development of new chambers on one side onl}^ (in such a 

 manner that the primordial segment seldom lies at the apex of the cone, but a Httle on one side 

 of it), and being then inclosed by an annulus formed by the gemmation of new segm.ents. In 

 Pla7iorhidt7Ui, however, each successive annulus is formed around the margin of the preceding, 

 from which every one of its segments derives stolon-processes ; whilst in Ci/iiibnlajjora each 

 new annulus is formed beneath the preceding, and has apparently no direct derivation from it. 

 The principal departure from the typical form is shown in the C. buUoides (Bosalina bulloides, 

 D'Orbigny, xcii). in which the whole of the base is occupied by a single large chamber, the 

 wall of which, instead of being furnished with its normal apertures, is perforated by numerous 

 large 'orbuline' lipped pores. 



377. Ajjiiiiiies:. — In the character and disposition of its earlier segments, and in the 

 asterigerine lamella at the base of its cone, Cymbcdopora ma}^ be considered as most nearly 

 related to Biscorbina ; but in the exchange of the spiral for the cyclical plan of growth, it 

 accords with Planorbnlina, differing from the last-named genus, however, far more than the 

 "wildest" of those forms to which we have extended its designation. 



378. Geographical and Geological Distribution. — The little Cgnibalopora is at present 

 restricted to the warmest seas, not being found in the Mediterranean, but being common in 

 the Ked Sea, in the East and West Indian Seas, and on the shores of the Fiji and other 

 Polynesian islands and of Australia. It frequents the Algal and Coralline zones and shell- 

 beds; and becomes small and irregular when presenting itself (as it not rarely does) at 

 depths of 500 fathoms. The only occurrence of this genus in a fossil form is in the 

 Maestricht beds, in which it presents itself in association with Calcarina and Biscorbina. Its 

 absence in the Tertiary strata of Europe (so far as is yet known) taken in connection 

 with the essentially tropical habitat of its recent representatives, is a fact of some 

 significance. 



Genus XVIII.— Calcarina (Plate XIII, fig. 21 ; Plate XIV, figs. 1—10). 



379. External Characters. — The name bestowed on this genus, of which the C. Spengleri 

 (the Nuutilm Spengleri of Linnaeus) is the typical form, is derived from the resemblance which 

 it presents in general aspect to the rowel of a spur (Plate XIV, figs. 1, 2), this resemblance 

 being produced by the divergence from the central disk of a set of rays or spines, which vary 



