of the Lower Malm of Aargau. 393 
a rare form of the Swiss Jurassic formation. As a rule, the 
Argovian specimens are more convex, and the surface more 
rough, though in every other respect they agree fully with 
Uhlig’s description. This variety.is chiefly interesting as it 
is more abundant in the younger zones of the Swiss Malm. 
Kiibler and Zwingli mention a similar form as Rotalina 
badensis from the zone of Terebratula impressa (Argovian II.). 
8. Lrochammina Reusst, Uhlig. 
The occurrence of this Upper Jurassic Trochammina in the 
Argovian deposits is still somewhat doubtful, as most of the 
forms resembling it can hardly be separated from the above- 
mentioned varieties. ‘The specimens in my collection are, asa 
rule, less involute; but in all the other characteristic features 
they agree with Uhlig’s 7. Reuss?. 
B. WEBBINA. 
Although Webbina seems to be present in almost every 
Jurassic zone, beginning with the Lias, only two or three 
species could be discovered, of which W. trregularis, Orb., 
and anew form, W. planorbiformis, were found in a few speci- 
mens in the Amm.-transversarius beds of the canton Aargau. 
1. Trochammina (Webbina) irregularis, Orb. 
(Pl. XV. fig. 15.) 
Test thin, fragile, finely arenaceous, one-or more-chambered; 
monothalamous variety consisting of a small pyriform or 
almost hemispherical chamber ; polythalamous variety straight 
or irregularly curved, consisting of few small rounded seg- 
ments joined by short stolons. Attached to the valves of 
Brachiopoda. Probably the one-chambered forms represent 
the earlier stage of the moniliform variety; they are very 
small (0°l millim.), always elongated at one pole, thus 
differing from W. hemispherica, J. & P.; the surface is also 
rougher than in the latter species. Some of the specimens 
answer well the description given by D’Orbigny, Carpenter, 
Jones and Parker, &c. 
2. Trochammina (Webbina) planorbiformis, sp. nov. 
(Pl. XV. figs. 16, 16 a.) 
Test serpuloid, forming in its earlier stage a regular spiral, 
in its younger part straight or irregularly bent. Typical 
specimens may be considered as fixed forms of 7’. centri- 
fuga, Brady; the others imitate the mode of growth of 
some Serpule found in the same zone (S. spirolinites, S. pla- 
4 
Ann. & Mag. N. Hist. Ser. 5. Vol. x. 
