REPORT ON THE FORAMINIFERA. 
57 
find the primary division of the Foraminifera into the Imperforata and Perforata still 
retained. His Sub-order Imperforata comprises all the chitinous and porcellanous 
genera, whilst the Sub-order Perforata is subdivided into the three Families of 
Carpenter’s classification. The distinctive feature of Zittel’s scheme is that the arenaceous 
forms have no independent position, but are distributed amongst the Porcellanea — 
part of them being assigned to the Family Cornuspiridce, the remainder to the Miliolidce. 
Such an arrangement does not commend itself, in view of the perforate tests of many of 
the sandy types ; and the appearance side by side, in the same Family, of genera as widely 
different as Botellina and Orbitolites, or as Nubecularia and Trochammina suggests 
some of the anomalies which it entails. 
The method of classification proposed by Dr. Schwager would leave little to be desired 
were the sole aim of the systematist the easy determination of the genera of doubtful 
specimens. An artificial system, indeed, has advantages over any other in this respect, 
and it would not be easy to construct a more orderly or more complete synopsis than the 
one furnished in Dr. Schwager’s modest paper. But, as has been before observed, the 
precision of definition suited to the comparatively stable characters of more highly 
organised animals can seldom be employed in the treatment of forms as variable as the 
Rhizopoda ; and in addition to their extreme variability, a further difficulty presents 
itself in the tendency to isomorphism amongst very distinct types. Thus it happens that 
in any artificial arrangement of the Foraminifera, closely allied genera are often widely 
separated, whilst others with no immediate affinity are thrown into juxtaposition. One 
or two examples from Schwager’s synopsis will serve to illustrate this point. We need 
not go beyond the first section, comprising “ calcareous, perforate Foraminifera, with 
segments disposed in one line and in one plane,” in which we find Nodosaria, Dentalina 
and Vaginulina, in three distinct Families, whilst Polymorpliina and Uvigerina are 
removed to quite another division of the table. Now, in point of fact, the connection 
between Nodosaria and Dentalina is so close, that it is not too much to say that many 
species are sometimes Nodosarian and sometimes Dentaline ; and the difference between 
some varieties of Vaginulina and Dentalina amounts to little more than a slight lateral com- 
pression of the shell. Of the position of Polymorpliina and Uvigerina in the same series 
I shall have to speak on a future page. So much for the separation of allied types. On 
the other hand, we find genera as diverse as Dentalina, Pidlenia, Polystomella and 
Nummulites all placed in the same Family ; — or to state the point somewhat differently, 
Dentalina is in nearer relationship with Polystomella than with Nodosaria ; and genera 
like Fusulina, Amphistegina and Heterostegina, come between Dentalina and Vaginidina. 
Similar anomalies, though perhaps few so striking as these, are to be met with in other 
sections of the table. In such cases natural affinity is sacrificed to the exigencies of a 
system — a heavy price to pay for its comparatively trifling advantages. 
Professor Biitschli’s synopsis of the Rhizopoda covers too large an area to invite 
