REPORT ON THE GENUS ORBITOLITES. 31 



figuriug an eight-tentacled polype as extending itself from one of its (supposed) open cells. 

 It was under the influence of his authority that, when I first puLlished (Quart. Journ. 

 Geol. Soc, 1849, p. 31) the results of my examination of the structure of the Australian 

 Marginopora (Orhitolites), in specimens collected by Prof. Jukes, and kindly placed in 

 my hands by Prof. Edward Forbes, I did not feel justified in calling its Bryozoic 

 characters in question, though I expressed myself doubtfully as to its claim to that 

 position. It was Prof. W. C. Williamson, as I have already pointed out (p. 5), who 

 first asserted the Foraminiferal nature of Orhitolites, on the basis of its near affinity 

 to the well-known Orbiculina adunca ; describing, under the designation OrbicuUna tonga, 

 what are clearly small specimens (only ^ of an inch in diameter) of Orhitolites com- 

 planatus, which he had obtained from shore-sand. This determination partly rested 

 on the structure of the central " nucleus " of the disks, which had been wanting in my own 

 specimens ; and of this Prof. Williamson gave a very accurate description, which I was 

 subsequently able to verify in the perfect specimens received from Prof. J. Beete Jukes 

 himself, as well as from other sources, — some of these having been preserved in spirit, and 

 containing the sarcodic body of the animal It was on these specimens that I based the 

 description of what I then distinguished as the " complex" type oi Orhitolites, which I 

 gave in my original Memoir on this genus (Phil. Trans., 18.56). And having lately -made a 

 careful re-examination, both of the shelly disks and of the sarcodic bodies of their contained 

 animals, collected by the naturalists of the Challenger on the slope and summit of the 

 Fiji reef, I am in a position not only to confirm that description in every particular, 

 but to add to it several particulars of much interest. 



It is probable that the younger and more delicate forms of Orhitolites complanata 

 habitually attach themselves to the surface of marine plants, the most perfect of those 

 which I received from Prof. Jukes, whose surfaces were nearly flat, having been found 

 thus attached ; and some of them being so thin in proportion to their diameter, that I can 

 scarcely think it possible that they could remain unbroken in the turbulent water of a 

 reef-slope if not thus supported. The case is diff"erent, however, in regard to those more 

 massive disks whose thickness increases as rapidly as their diameter, so that they 

 become more or less deeply biconcave ; for as such could only adhere at their margins, 

 they must be liable to become easily detached ; and as they are brought up alive by the 

 dredge, they probably go through the later stages of their growth in the free condition. 

 That such must be the case in regard to these large, irregular, " laciniate " forms, of which 

 examples are figured in PI. VII., is very obvious ; and I learn that the specimens of 

 these which contain the coloured sarcodic body were taken alive from sheltered nooks 

 in rock-pools on the summit of the reef, while the dead specimens (distinguished by 

 their absence of colour) were picked up on its surface. 



It is of the disks of this species that the great bulk of the Challenger collection on 

 the Fiji reef is composed ; and these disks present a range of diameter from 0"04 inch, 



