138 
THE VOYAGE OF H.M.S. CHALLENGER. 
on the other hand, most of the Quinqueloculince have a Triloculine stage of growth. Under 
d’Orbigny’s definitions young specimens and adults of the same variety have over and over 
again been placed as distinct species in separate genera. Amongst smooth-shelled forms 
the anomaly might pass unnoticed, but amongst those in which peculiarity of surface- 
ornamentation affords the principal distinctive character the double nomenclature becomes 
palpably absurd. There is still another objection to these generic terms, which is 
brought into stronger light than heretofore by specimens obtained from the Challenger 
dredgings, namely, that the number of exposed segments is not necessarily either three or 
five. In one striking subarenaceous species, Miliolina alveoliniformis, there are often 
seven or eight, long, narrow chambers in the peripheral whorl ; and in another arenaceous 
form, Miliolina triquetra, instead of two segments, one up and one down, forming the 
axial circuit of the test throughout, there are usually three segments in the final circuit of 
adult shells, the contour becoming flattened as in Spiroloculina, and more or less tri- 
angular. Neither of these could be included in any of the Milioline genera as hitherto 
constituted. Instances of the same sort might readily be multiplied, but enough has been 
said to show that Triloculina and Quinqueloculina may properly be discarded as generic 
or even subgeneric names, just as Adelosina was long since abolished and for similar 
reasons, and that some general name less open to objection should be found for this 
portion of the group. Prof. Williamson, after discussing the question with his usual 
acumen , 1 adopts the term Miliolina for the section under consideration, and with a slight 
modification of the characters assigned to it in his Monograph, its general adoption would 
be a distinct gain to systematic zoology. 
The position taken by Parker and Jones is unassailable, viewed from a strictly 
biological standpoint. The great diversity amongst Foraminifera in the comparative 
constancy and distinctiveness of the minor peculiarities wdiich characterise the sub- 
ordinate forms has already been adverted to. Many instances might be cited in which 
apparently trivial characters are as reliable and as little subject to variation as those of 
animals more highly organised, but such is not the case amongst the Miliolce. The 
successive modifications merge one into the other so as to constitute an almost unbroken 
series, and the task of the zoologist resolves itself into the selection of the salient forms most 
suitable for quasi-specific names. Under these circumstances, the term Miliola may very 
properly be used in a generic sense to comprehend a great variety of closely associated 
forms having the same general type of structure ; whilst Biloculina , Spiroloculina, and 
Miliolina represent subordinate divisions, under which, for more easy identification and 
for convenience of nomenclature, it is necessary to arrange them. 
1 Recent Foraminifera of Great Britain, p. 83. 
