50 Dr. R. Haeusler on the Trochamminz 
A comprises the oldest sediments of the zone, covering the 
Ornatus-beds of the Callovian, with predominant limestones 
and a richly developed fauna of Cephalopoda. — 
B, the beds with lithologically analogous character, and 
numerous Brachiopoda and Crinoidea. 
-C comprises the youngest marly beds with Nulliporites and 
few animal remains. diate 
According to these artificial subdivisions the microscopical 
fauna is different: the arenaceous Foraminifera, chiefly the 
Trochammine, reach their maximum development in the 
lowest beds A, where they are associated with Lituola 
(Haplophragmium, Haplostiche, Placopsilina), Endothyra, 
Plecanium, and other arenaceous and hyaline species (Nodo- 
saria, Dentalina, Oristellaria, &c.). In many cases the un- 
favourable condition of the minute shells, caused through 
pseudomorphoses, incrustration with iron-pyrites, or atmo- 
spheric influences, makes the determination of the species im- 
possible. 
The Foraminifera mentioned in this paper were obtained 
from materials collected during a twelve-years’ stay in the 
Canton Aargau, from all the different localities where the zone 
is exposed, but principally from the following :—Staffelege 
(near Aarau), Densbiiren, Auenstein, Kreisacker, Biren, 
Hottwyl, Hornussen, Bézen, Mandach, Villigen, Birmenstorf, 
Schambelen, &c. 
The oldest known arenaceous Foraminifera of the Swiss 
Jurassic formation are some rare placopsiline Lituole attached 
to the shells of Gryphea, Pecten, and Ammonites of the Lower 
Sinemurian beds, where they occur with numerous varieties 
of Nodosaria, Dentalina, Marginulina, Cristellaria, &c. 
Trochammina appears for the first time in the Bajocian, 
and ranges from here through the whole Upper Dogger, but 
only in two species (Z. incerta and T. jfilum). With the 
Lower Malm the arenaceous and some other Foraminifera 
become more abundant, so that these beds have yielded up to 
the present time almost as many species and varieties as the 
rest of the Swiss Jurassic formation together. 
In these sediments all the principal types of the genus 
Trochammina axe well represented; most of them disappear 
suddenly towards the Middle Sequanian beds. Some of them 
are only known from the beds A of the éansversarius-zone ; 
T. incerta and T. gordialis are occasionally met with in the beds 
C and the zone of Terebratula impressa. ‘The Upper Argovian ° 
limestones, with a more littoral fauna of numerous Wye 
(Pholadomya, Goniomya, &e.), contain several of the Tro- 
chammine of the Lower Argovian (7. incerta, T. gordialis, 
