52 Dr. R. Haeusler on the Trochamminz 
convolutions (four or five) passing into the conical and Quin- 
queloculina-like species and 7’. filum. ; 
Both varieties run into each other through numerous inter- 
mediate forms with regard to the mode of growth and the 
composition of the shell. The division is therefore entirely 
artificial, but so far quite justifiable as it prevents us from 
uniting the most heterogeneous forms under one name, and 
from making thus a clear description quite impossible. 
T. incerta irreg. may be divided into several subvarieties, 
as the forms resembling 7. ¢ncerta reg., or those differing. 
from J’. gordialis merely by the discoidal obvolution of the 
tube, corresponding to Cornuspira variabilis, K. & Z., or as 
those identical with C. crassa, K. & Z, It is, however, 
impossible to draw lines of separation—the more so as hardly 
two specimens are alike, the great number of these one-cham- 
bered. Trochammine forming an unbroken chain of nearly- 
related individuals, passing from T. incerta typ. into the 
conical and even polythalamous species. As a rule, it may 
be said that the more the shell differs in its external appear- 
ance from the typical 7. incerta reg. of this zone, the greater 
becomes the mass of sandy constituents compared with that 
of the siliceous or calcareous cement. Most of the specimens 
of this species answer the description of Orbis, Involutina, 
and Ammodiscus given by Strickland, Terquem, Reuss, and 
Bornemann ; but many of the conical specimens consisting 
of a similarly built-up test, and the compact limestones of the 
Upper Argovian étage containing undoubtedly shells with 
calcareous cement, all these and some similar forms known 
as Spirilline, Operculine, Cornuspire, must be united to the 
genus Trochammina, as, indeed, was done long ago by English 
geologists. 
A. Trochammina incerta reg.* (Pl. IIT. figs. 1-4.) 
Test free, regularly convoluted or partly involuted, dis- 
coidal, formed of a simple non-constricted imperforate tube, 
regularly increasing in width. 
Convolutions six to eight in one plane, sometimes embra- 
cing; aperture large, at the non-constricted end of the tube ; 
test thin, transparent, built up of almost hyaline siliceous shell- 
matter and afew very minute grains of sand. Surface smooth, 
sometimes brilliant, and with small more or less regularly 
distributed depressions, which, when examined with a. low 
power, take the appearance of perforations, and give the shell 
a resemblance to Spirillina. 
* The descriptions given only refer to the Foraminifera of the ¢trans- 
versarius-zone of the Aargau, if not stated otherwise. 
