CONSTITUTION OF CHALK AND FLINT. 
153 
researches in this group of Rhizopods, and we are enabled to 
compare the living and fossil forms with more exactitude than 
heretofore. The Foraminifera being of simple structure and lowly 
life, and capable of existing under a great variety of conditions, 
have a somewhat similar appearance throughout all faunae in which 
they occur; nevertheless there is a peculiar and local facies in each 
separate and successive group, besides the presence or absence, 
abundance or paucity, of particular genera and species. The Fora- 
minifera of the Chalk have their own well-marked facies , and 
there are relatively few species or notable varieties living now that 
lived in the Chalk-sea. Taking the North-Atlantic alone, its fauna 
at present comprises about 5 per cent, of the Cretaceous species of 
Foraminifera, and its Molluscs and Echinoderms are far from being 
the same as those of the Chalk. Moreover, the Foraminifera seem 
to he of such growth and aspect as are usually presented among 
Foraminifera living at far less than abyssal depths; and with this, 
as we have already noted (page 148), the Molluscs are said to agree. 
An interesting point in the study of Foraminifera is a recognition 
of those which, living only at or near the surface of the ocean, 
have been termed “ pelagic,” as distinct from those which live on 
the sea-bed. It became of late years almost a party-question as to 
whether Globigerince were solely ‘‘pelagic” or not. The species 
known for certain to have been taken at the surface are— 
Globigerina bulloides , d’Orb.* Globigerina rubra , d’Orb. 
- dubia , Egger. - sacculifera, Brady. 
- marginata (Reuss).* - conglobata , Brady. 
•-— inflata , d’Orb. - cequilateralis, Brady. 
(Eight out of sixteen species in H. B. Brady’s ‘ Report.’) 
Orbulina universa, d’Orb A Pulvinulina tumida , Brady. 
Bastigerina pelagica (d’Orb).* - Canariensis (d’Orb.). 
Pullenia obliquiloculata, P. and J. --- crassa (d’Orb.). 
Sphceroidina dehiscens, P. and J. - Micheliniana (d’Orb.).* 
Pulvinulina Menardii (d’Orb).* 
(Five out of thirty-two in H. B. Brady’s ‘ Report.’) 
The following are less certainly “ pelagic ” : — 
Candeina nitida, d’Orb. Cymbalopora bulloides (d’Orb.). 
Pulvinulina Patagoniea (d’Orb.). Chilostomella ovoidea , Reuss.f 
It is doubtful—(1) whether some of these, if not all, can and do 
live at the bottom as well as near the surface;—(2) whether or no 
there are differences of structure in two series of each species, one 
for “pelagic,” and one for deep-water existence;—and (3) whether 
some have only a temporary breeding-time during “pelagic” life. 
Doubtless an enormous variety of other Foraminifera do exist on 
the sea-bed, often at very great depths ; and there is no reason to 
doubt that those of the Chalk were chiefly of this kind. 
* These are known in the Chalk. 
+ See H. B. Brady’s ‘ Report,’ etc., pp. x, and following, for his remarks on 
the “pelagic” Foraminifera, with references to other observers and writers on 
the same subject. 
