EORAMINIFERA OF THE KEEIMBA AECHIPELAGO. 605 



But the examination of a large series of specimens from a locality such as the 

 Kerimba Archipelago, where both species are equally abundant, tends to show that 

 these features, though perhaps generally, are not universally consistent, for we have 

 found unquestionable examples of 0. marginalis presenting both single and double 

 pores in different parts of the periphery of the same specimen, and also presenting 

 the usual orbiculine initial portion in such minimum stage of development as to be 

 practically inseparable from the postulated commencement of 0. duplex. The specific 

 distinctiveness of the two forms appears to us, therefore, to remain open to some doubt, 

 and the question arises whether they may not be stages in the life-history of the same 

 organism, perhaps forms A and B of a dimorphic series. 



119. Orbitolites duplex Carpenter. 



OrhitoUtes duplex Carpenter, 1856, etc., RF. 1856, p. 220, pi. v. fig. 10, pi. ix. fig. 10. 



„ „ Carpenter, 1883, RGO. p. 25, pi. iii. figs. 8-14, pi. iv. figs. 6-10, pi. v. 



figs. 1-10. 

 Erady, 1884, FC. p. 216, pi. xvi. fig. 7. 

 „ „ Heron-Allen & Earland, 1908, etc., SB. 1909, p. 320. 



15 Stations. 



Almost universally distributed, and common at some Stns. The best specimens 

 Avere at Stns. 2 h and 9. Under 0. marginalis we have dealt at length with the 

 specific characters of this species. In its optimum development there is no difficulty 

 in the identification of a specimen of 0. duplex; it is only in the younger and more 

 feebly developed specimens that any hesitation is experienced. 



The Kerimba specimens of 0. duplex are subject to much more variation than 

 0. marginalis ; double and irregularly built individuals were observed at Stn. 11. At 

 Stn. 7 the process of repair was also noticed, and at this Stn., at % B, and several others, 

 the larger specimens exhibited a tendency to an abnormal and sudden increase in the 

 size of the chambers in the outer annuli, which were often inflated and very thin- 

 walled, the appearance of such a test being like a circular pan or dish with a raised 

 and thickened rim. It is possible that this feature may represent the commencement 

 of the brood-stage, but we have been unable to find any specimens containing 

 primordial young such as we have found in 0. complanata. 



Many of the specimens, both of 0. duplex and 0. complanata, exhibit growths of 

 secondary shell-matter usually radiating in bands from the centre of the test, as figured 

 by Carpenter (C. 1856, etc., EF. p. 217, pi. vii. figs. 10, 11). These outgrowths, which 

 are usually of a denser and more porcellanous character than the rest of the shell, 

 probably merely mark excessive shell-development under exceptionally favourable 

 conditions. Symbiotic algae were observed in all three species of OrhitoUtes, in some 

 cases in such numbers as to give a greenish tinge to the whole shell, as described by 

 Moseley in his " Notes by a Naturalist on the 'Challenger'" (London, 1879, pp. 292-3). 



