of the Lower Malm of Aargau. ol 
LT. filum, T. jurassica), which mount into the beds of the 
Lower Sequanian (zone of Am. bimammatus and Hemicidaris 
crenularis), where chiefly one small layer with numerous spines 
of Rhabdocidaris caprimontana is noticeable for the small but 
well-preserved microscopic shells. 
It is very probable that these compact limestone sediments, 
formed under somewhat similar conditions as those of 
the lower Birmenstorf Schichten (chiefly the beds crowded 
with Hexactinellid sponges), may contain all the species of 
the latter, which, owing to the difficulty of collecting them, 
have not yet been found. The higher beds of the Malm have 
not yet been carefully examined; but from the few micro- 
scopic specimens from the Middle and Upper Sequanian and 
the Kimmeridge group, it seems that 7. incerta and T. gor- 
dialis are the only representatives of the genus. These were 
also found in the Sequanian of Olten, Solothurn, and Ste. Ur- 
sanne, and in the Kimmeridge beds of the neighbourhood of 
Pruntrut. 
The few pieces of Alpine Upper Jurassic rocks which I 
examined, and which offer the least favourable condition for 
microscopical researches, did not yield any traces of Forami- 
nifera. 
Trochammina incerta, O. 
This species is, as a rule, not common in the Swiss Jurassic 
formation ; but it is the most remarkable from its wide geo- 
graphical and geological distribution. It is present in every 
étage from the Bajocian up to the Kimmeridgian. It always 
presents very much the same appearance and the same 
typical varieties, not considering alterations of the shell 
through atmospheric action; while probably all the other 
species of Zrochammina differ considerably when found in 
beds with entirely different constituents and organic remains. 
According to the composition of the shell and the mode of 
growth, this species can be divided into two distinct varieties. 
In the one, which, for convenience, we may call Zr. incerta 
reg., the test is thin, more or less transparent, built up of a 
generally siliceous cement and a minimum quantity of foreign 
sandy matter. 
In the second (7. incerta irreg.) the test is thicker, not 
transparent, and built up of numerous small particles of 
quartz-sand imbedded in a whitish or ferruginous cement. 
T. incerta reg. comprises almost invariably the more 
regularly convoluted larger specimens, with from six to eight 
convolutions lying in one plane, similar to Spirdllina arenacea, 
Will.* ; 7. incerta irreg. the smaller irregular forms with few 
* Williamson, Rec. Foram. Brit. p. 93, pl. vii. fig. sie 
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