DE. 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 Aegean, 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 0. 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 liis “ Paleontologia del Regno di Napoli,” part ii., in ‘Atti dell’Accad. Pontan,’ vol. vii., 
P- 178, plate xvi., figs. 26-28, 
4 c 2 
