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214 TH E A T L A N T IC .
may almost always be made out Avitli a high power.
Tliere never are spines on tbe GlohigerincB from tlie
f 1
F ig . i l .— Orbulina u n iv e r sa , D'Oubiony. From the surface. F ifty times tlie n a tu ra l size.
bottom, even in the shallowest water. Two or three
very marked varieties of Globigerina occur; hut I
certainly do not think that the characters of any of
them can he regarded as of specific value.
There is still a good deal of obscurity ahout Die
nature of Orbulina universa, an organism which
occurs in some places in large proportion in the
glohigerina-ooze. The shell ot Orhulina (big- 47) is
spherical, usually ahout '5 mm. iu diameter, hut it is
found of all smaller sizes. The texture of the mature
shell resembles closely that of Glohigerma, hut it
differs iu some important particulars. The pores are
markedly of two different sizes, the larger about four
times the area of the smaller. The larger pores are
the less numerous ; they are scattered over the sui-
face of the shell without any appearance of regularity ;
the smaller pores occupy the spaces hetween the
larger. The crests between the pores are mucli less
regular in Orhulina than they are in Glohigerina;
aud the spines, Avliich are of great length and extreme
tenuity, seem rather to arise abruptly from the top of
scattered papillm than to mark the intersections of
the crests. This origin of the spines from the papillm
can he well seen with a moderate power on the periphery
of the sphere. The spines are hollow and
flexible ; they naturally radiate regularly from the
direction of the centre of the sphere; but even in
specimens which have been placed under the
microscope with the greatest care, they are usually
entangled together in twisted bundles. They are so
fragile that the iveight of the shell itself, rolling about
Avith the motion of the sliip, is usually sufficient to
break off the whole of the spines and leave only the
papilla) projecting from its surface, in the course ot
a few minutes. In some examples, either those in
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