626 
THE VOYAGE OF H.M.S. CHALLENGER 
sides are equally or unequally convex ; in others, again, both are complanate or slightly 
concave ; and in some the superior face is flat and the inferior convex. These conditions 
are variably represented in the four genera under consideration. 
The annexed Table, in which a number of species from each generic group are cast 
into parallel columns, is intended to illustrate broadly the isomorphism which has been 
described. It serves also to show the general contour of test most prevalent in the 
different genera. For example, it indicates that Discorbina is rich in forms with convex 
or conical superior face, whilst it has but few that are convex and none that are conical 
on the inferior side, and no evolute or wild-growing adherent species ; that Planorbulina, 
on the other hand, has scarcely any varieties with the superior side convex or conical ; 
that Pulvinulina has nothing corresponding to the complanate or bilaterally sym- 
metrical modifications of the other genera ; and that Rotalia, with its fewer species, is 
almost entirely wanting in evolute, adherent, and wild-growing forms. Two lines have 
been added to the Table to show that the parallelism extends to other particulars, such as 
the external limbation of the sutures, and the extension of the margin of the test into 
radial points or spines. The scheme might be extended in many ways. An additional 
column might be assigned to the genus Cymbalopora, though the number of species is 
comparatively small and their range of variation correspondingly limited, and an interest- 
ing collateral series might also be drawn from the genus Globigerina ; but the object of 
the Table is sufficiently attained without further expansion. 
It would be manifestly impossible to frame zoological descriptions based upon the 
conspicuous features of the test that would avail to separate genera constructed on lines 
so nearly identical ; and it is from characters other than those derived from the form and 
mode of combination of the segments that means of distinction are to be sought. 
Such characters do exist, though they are often ill-defined and always variable. For 
example, the genus Discorbina may pretty constantly be recognised by the presence, in 
one form or other, of certain projections from the inner margins of the segments on the 
inferior side, known as “ umbilical lobes,” more fully described on a later page ; or, when 
these are not apparent, by a surface-ornament of radiating costae or lines of closely-set 
granules. The Planorbulince , of all sections of the group, are known by their coarsely 
porous thick- walled tests, and a tendency to produce lipped apertures, the orifice of the 
superior to a surface which in the living creature is so obviously inferior , I have not thought it desirable to disturb the 
general application of these terms to meet so exceptional a case.” — Brit. Rec. Foram., Introd., pp. xvi, xvii. 
This rule is by no means free from objection ; but perhaps it would be impossible to devise one in all respects 
satisl’actory. The employment of the terms in a manner equally available for the elongate spiral types, such as Bulimina 
and Textularia, and moniliform shells like the Nodosarice, would have been in many ways preferable. These latter 
forms are always represented pietorially with the primordial segment at the base and the growing-point at the summit ; 
and by Williamson and others the terms posterior and anterior are employed for them respectively ; so that posterior 
becomes the equivalent of superior and anterior of inferior , which is somewhat anomalous. In a large number of cases 
the words spiral and umbilical may properly be used, as an alternative, for the two aspects of the Rotaline shell, hut 
they are not quite uniformly applicable. 
