DR. W. B. CARPENTER ON ORBITOLITES TENUISSIMA. 559 



dredging taken by the French exploring-ship " Travailleur " in the Bay of Biscay 

 (Fosse de Cap Breton), at a depth of 1,200 fathoms. 



It would seem, therefore, that Orbitolites tenuissima has its proper home on the 

 sea- bottom of the deeper parts of the North Atlantic, where the temperature ranges 

 from 37 to 35 Fahr. ; but that it also is capable of living, not only in much 

 shallower, but also in much warmer, waters. For the temperature of the Mediter- 

 ranean and ^Egean, even at depths below 100 fathoms, is never less than 54, while 

 on the shallow bottom of Setubal Bay, and on the shore-slope near Carthagena, the 

 summer temperature must be considerably higher. 



Looking to the singular retention, in this beautiful Orbitoline, of the Milioline type 

 from which its derivation may now be confidently affirmed, the probability seems 

 strong that it was a very early form ; and if identical with COSTA'S Pavonina italica* 

 as the imperfect account given by him of that type would seem to indicate, it probably 

 inhabited the Mediterranean during the greater part of the Tertiary period. Its 

 persistence in the abyssal depths of the North Atlantic harmonizes well with the idea 

 of its antiquity ; those depths having been found, by the recent exploration of them, 

 to be inhabited by many " survivals " of the Cretaceous and even earlier Faunae. It 

 may be remarked, finally, that the considerable diameter attained by these very fragile 

 discs, seems a proof of the extreme tranquillity of the deep-sea bottom ; since they 

 could not otherwise have gone on growing and extending themselves, without showing 

 more frequent marks of injury and reparation than I have observed in them. 



Relation to other Orbitoline Types. 



Having been requested by the late Sir C. WYVILLE THOMSON to prepare a Report 

 on the Orbitolites collected in the " Challenger " Expedition, I have carefully studied 

 the remarkable gatherings made of them on and near the summit of the Fiji reef, 

 and also at a depth of 18 fathoms on its slope. The result of that examination now 

 enables me to indicate with great probability the successive stages of the evolution of 

 that highly specialised " complex " type, the derivation of which from a Milioline 

 ancestry would have seemed but for the completeness of the series of intermediate 

 forms almost inconceivable. And I can now also mark out, with more distinctness 

 than formerly, the types of this Genus, which, in virtue of their constancy and 

 definiteness, are entitled to rank as distinct species. 



The first of these is the O. marginalis of Lamarck, known to him only by small 

 Mediterranean specimens of no more than two millims. (about 0'08 inch) in diameter, 

 but attaining on the Fijian reef a diameter of 0'2 inch, and presenting a much more 

 characteristic aspect than is discernible in the dwarfed Mediterranean form. The well- 

 developed "cycloline" disks of this beautiful form of the "simple" type (fig. I., 1), 



* See his " Paleontologia del Regiio di Napoli," part ii., in 'Afcti dell' Accad. Pontan,' vol. vii., 

 p. 178, plate xvi., figs. 26-28. 



4 c 2 



