606 
THE VOYAGE OF H.M.S. CHALLENGER. 
number, and all visible from either side of the shell, nearly globular in shape, the last 
sometimes smaller than the penultimate ; aperture a large arched opening on the umbilical 
face of each segment. Diameter, g^th inch (0'84 mm.), more or less. 
Globigerina cequilateralis is the type of the planospiral as distinct from the Rotaliform 
varieties of the genus. It approaches Hastigerina in general contour, but the arrange- 
ment of the chambers is usually if not invariably evolute instead of involute, and the 
shell-wall is relatively much thicker than in the latter genus. The test is somewhat 
finely porous, the perforations measuring about ^y^th to ■ 3 - 0 1 0 - T) -th inch (0‘0042 to 0‘005 
mm.) in diameter. So far as has been observed, the surface specimens do not manifest to 
the same extent as those of many other species the tendency to assume a spinous 
condition. 
Globigerina cequilateralis occurs amongst the surface-microzoa from the North Atlantic 
and the North and South Pacific. It has also been found in the South Atlantic but 
only in bottom-dredgings. Its area of distribution appears to extend from off the south- 
west corner of Ireland, lat. 50° N., to the Cape of Good Hope, about lat. 35° S. 
There can be little doubt that one of the specimens figured by Egger under the 
name Cassidulina globulosa belongs to the present species, so that its geological history 
dates back at least as far as the Miocene period. Ehrenberg gives a drawing of a very 
similar form, possibly the same ( Phanerostomum asperum, Mikrogeologie, pi. xxx. 
fig. 26, a.b.) from the Chalk of the Island of Rugen. 
Orbulina, d’Orbigny. 
Orbulina, d’Orbigny [1839], Reuss, Bailey, Costa, Williamson, Parker and Jones, Karrer, 
Carpenter, Wallicb, Seguenza, Terquem, Brady, Alcock, Dawson, Fischer, &c. 
Miliola, pars; Monocystis, Ehrenberg [1854]. 
Globigerina, pars, d’Orbigny [1846], Pourtales, Reuss, Alcock, Owen, Brady, Seguenza. 
The genus Orbulina was first brought into notice by d’Orbigny in his memoir on 
Cuban Foraminifera, but the author appears to have been previously well acquainted 
with the typical species from specimens collected on the shores of the Adriatic and else- 
where. 
The original generic description runs as follows “ Shell free, regular, spherical, 
globular, interior hollow ; pierced in every part by a large number of minute pores only 
visible when highly magnified ; aperture small, rounded, placed at a point of the 
circumference ; ” to which is appended the remark “ it is possible that under certain 
circumstances the animal is able to close the aperture of the shell, at any rate it is not 
always visible, and it is only open in one-sixth of the freshly collected specimens ” 
(Foram. Cuba, p. 34). 
Williamson states that “ the septal aperture of Orbulina universa is small ; normally 
