CHAP. III. ] TENERIFFE TO SOMBRERO. 209 
prolonged downward, so that the shell is deeper and somewhat 
turbinate. The two species usually occur together, but P. M:- 
cheliniana has apparently a much wider distribution than P. 
Menardii; for while the latter was limited to the region of 
the trade-winds and the equatorial drift current, and was found 
rarely, if at all, to the south of the Agulhas current, the 
former accompanied us southward as far as Kerguelen Land. 
Both forms of Pulvinulina, however, are more restricted than 
Globigerina; for even P. Micheliniana became scarce after 
leaving the Cape, and the wonderfully pure calcareous for- 
mation in the neighborhood of Prince Edward Island and the 
Crozets consists almost solely of Globigerina bulloides, and nei- 
ther species of Pulvinulina occurred to the south of Kergue- 
len Land. 
Over a very large part of the globigerina ooze area, and es- 
pecially in those intertropical regions in which the formation 
is most characteristically developed, although the great bulk of 
the ooze is made up of entire shells and fragments of shells of 
the above-described foraminifera, there is frequently a consider- 
able proportion (amounting in some cases to about twenty per 
cent.) of fine granular matter, which fills the shells and the in- 
terstices between them, and forms a kind of matrix or, cement. 
This granular substance is, like the shells, calcareous, disappear- 
ing in weak acid to a small insoluble residue: with a low micro- 
scopic power it appears amorphous, and it is likely to be regard- 
ed, at first sight, as a paste made up of the ultimate calcareous 
particles of the disintegrated shells; but under a higher power 
it is found to consist almost entirely of ‘coccoliths” and ‘“ rhab- 
doliths.” I need scarcely enter here into a detailed description 
of these singular bodies, which have already been carefully stud- 
ied by Huxley, Sorby, Giimbel, Haeckel, Carter, Oscar Schmidt, 
Wallich, and others. I need only state that I believe our obser- 
vations have placed it beyond a doubt that the “ coccoliths” are 
the separated elements of a peculiar calcareous armature which 
