590 
THE VOYAGE OF H.M.S. CHALLENGER. 
Introduction to the Study of the Foraminifera j 1 and more briefly, but in the same sense, 
by Parker and Jones in their memoir on Foraminifera from the North Atlantic and Arctic 
Ocean, as follows : — “ The shell of Globigerina is composed of a series of hyaline and 
perforated chambers, of a spheroidal form, arranged in a spiral manner, and each opening 
by a large aperture around the umbilicus, in such a manner that the apertures of all the 
chambers are apparent on that aspect of the shell, and form a large c umbilical vestibule.’ ” 2 
This umbilical vestibule, into which “ each segment opens by a large crescentic orifice, 
the several chambers having no direct communication with each other,” is a feature of some 
prominence in Carpenter’s description. 
Parker and J ones, in their paper above quoted, record the occurrence of only two 
species of Globigerina, namely, the typical Globigerina bulloides and Globigerina injlata ; 
and in their supplementary tables recognise but two others, Globigerina helicina and 
Globigerina hirsuta. The allusions in Dr. Carpenter’s work are confined to the same 
forms. This paucity of illustration must be attributed to the fact that the researches of 
the authors referred to were based chiefly upon the northern representatives of the type ; 
and the limited view which they adopt as to the generic characters of the group results 
more or less from the same circumstance. 
Owing to the wide area embraced by the dredging operations and the diverse 
conditions under which the tow-net was employed, the Challenger collections have 
opened a new field for the investigation of the genus ; and its morphological characters 
have been found to present a far wider range of variability than seems to have been 
previously suspected. 
With rare exceptions, which need not at present be taken into account, the test of 
Globigerina is always distinctly spiral. In the typical Globigerina bulloides and its 
immediate allies it is constructed on the Rotaline plan, that is to say, the whole of the 
segments are visible on the superior face of the shell, those of the last convolution only 
on the inferior; but in certain forms, of which Globigerina cequilateralis is the most 
important, the arrangement is planospiral, and the segments are seen equally on both 
faces of the test. The general external contour of the shell is either conical, trochoid, 
turbinoid, subglobular, nautiloid, plano-convex, compressed and carinate, or complanate. 
The number of segments of which the adult shell is composed, varies in different 
species from three to about twenty, and they are arranged so as to form from one to three 
convolutions. The individual chambers are typically spherical, and they are separated 
externally by deep depressions ; but in the compact varieties of the genus they are 
not more convex externally than those of other Rotaliform Foraminifera. In certain 
cases part of the segments of the outer convolution are elongated radially and have 
pointed extremities, whilst in others the chambers are compressed and their sutures 
occasionally limbate. 
1 Introd. Foram., p. 181. 
2 Phil. Trans., 1865, vol. civ. p. 365. 
