350 Dr. R. Hiusler on the Trochammine 
of intermediate forms or ‘ missing links,” by which the great 
number of multilocular varieties can be united in one un- 
interrupted chain of imperceptible gradations. Nevertheless 
we always come across typically built individuals, from which 
we are able to recognize the previously recorded species. 
Beginning with the simplest septate 7’. constricta—which, 
with a minute variety of 7. coronata, agrees in the composi- 
tion of the delicate tests with 7. (Ammodiscus) incerta—we 
arrive at the conclusion that the more the species differ from 
those primitive types the more the shells become proportionally 
coarsely sandy, finishing the series with 7’. helveto-jurassica. 
An analogous change distinguishes also the more complicated 
Ammodisct from the simple planispiral varieties. 
It would be absolutely impossible to consider all the diffe- 
rent varieties without’ taking notice of specimens from the 
Upper Dogger and the younger zones of the Malm, which for 
the present we cannot include in this short paper. Much 
work has still to be done to obtain a complete knowledge of 
the innumerable modifications as results of adaptation to con- 
siderable changes in the configuration of the sea-bottom. 
The more we become acquainted with the microscopical 
faunas of the Jurassic formation, the more the difficulties of 
fixing true species increase ; yet, on the other hand, the resem- 
blance of many Jurassic forms to those obtained from the 
recent deep sea offers interesting examples of the constancy 
of certain types, from which countless varieties have developed 
themselves during enormous intervals of time. 
The fact that many arenaceous Foraminifera were first de- 
scribed as hyaline forms altered by a replacement of the 
carbonate of lime by silica, can easily be accounted for by the 
presence of other organic remains which had undergone 
complete changes, as, for instance, Polyzoa, Echinoderms, 
and Mollusks, while the siliceous sponges were transformed 
into carbonate of lime or iron-pyrites. 
A. Trocuammina, J. & P. 
The multilocular rotaline Trochammine belong to the whole 
Jurassic formation, though in the Lias and Lower Dogger 
they are only known in one minute form, probably an inter- 
mediate form between 7. squamata and T. inflata. Like 
Ammodiscus, they first appear in greater number in the Ba- 
thonian stage, and reach their maximum development in the 
Lower Malm. From the zone of Ammonites transversarius 
the following species were obtained :— 
