GENUS CYMBALOPORA. 215 



from the Levant. It has not yet been found in the Arctic seas, and it is neither abundant 

 nor of more than half its ordinary size on the British coasts ; on the other hand, it is in tropical 

 specimens that we find it most thickly clothed with exogenous deposit, and its canal system 

 most developed. It does not flourish in deep waters, its size being reduced to less than one 

 fourth at a depth of 100 fathoms ; whilst its form is altogether changed, and it becomes very' 

 small and rare, at 1000 fathoms. On the other hand, it extends far up estuaries and into 

 salt-bogs — No true Rofaliie are at present known to have existed earlier than the Chalk, in 

 which formation there occur examples of B. Bcccarli whose small size indicates that they 

 lived at considerable depths, probably from 100 to 400 fathoms. It is in the Tertiary forma- 

 tions, however, that this sub-genus occurs in greatest abundance ; some shallow water-beds 

 of the Crag and of the Siennese deposits being almost entirely composed of Bolalice. 



Genus XVII.— Cymbalopora (Plate XIII, figs. 10—12). 



375. External Characters and Internal Structure. — This small genus,including only four spe- 

 cific forms hitherto described, was instituted in 1850 by Hagenow (" Die Bryozoen der Maas- 

 trichter Kreide-bildung") on the basis of a minute fossil which he supposed to be a Bryozoon, 

 but which has been found by Messrs. Parker and llupert Jones to agree in structure with 

 the Bosalina Poei/i of D'Orbigny (xcii), a type distinguished by peculiarities of conformation 

 quite sufficient to differentiate it from all other genera of the Rotaline sub-family. All the 

 examples of this genus are of comparatively small size ; the diameter of the largest of them (fossil 

 from the Upper Chalk of Maestricht) being not more than l-18th of an inch ; whilst that of 

 the ordinary specimens obtained from deep water at the present time does not exceed l-120th 

 of an inch. When seen from the superior lateral surface, or looked at edgeways (Plate 

 XIII, fig. 10), a Cymbalopora does not present any marked feature that distinguishes it from a 

 trochoid Biscorhina, save that the spiral arrangement of its segments does not appear to be 

 continued with regularity as the cone enlarges. But when its inferior surface is examined, a 

 very extraordinary departure from that regularity displays itself; for we there find its seg- 

 ments arranged concentrically around a deep umbilical vestibule, which extends far up into 

 the cone. Sometimes these segments are numerous and narrow, and being as it were 

 wedged in between the segments of the preceding layer, they are separated from each other 

 by considerable intervals (Plate XIII, fig. 11). But in other cases they are few in number 

 (the whole annulus being made up of only four or five), broad, and flat ; and the interval between 

 them is reduced to a flssure (fig. 12). In either case each segment communicates with the 

 umbilical vestibule by a prolonged tubular neck ; and it also has two large lipped orifices on 

 either side, apparently for the passage of sarcode-stolons to the adjacent segments. Tl>e 

 shelly lamina which forms the basal walls of these segments is much more hyaline and less 

 porous than that which bounds them externally ; and we notice the homologue of the asteri- 

 gerine flaps of Discorhina in the frequent extension of a lamella of shell over the umbilicus, 

 closing-in its cavity, and connecting together the internal necks of the segments. It can 

 scarcely be doubted that this umbilical cavity is occupied in the hving condition by a portion 

 of the sarcode body of the animal ; and that from this are put forth by gemmation the seg- 



