134 GENESIS OF THE ARIETID. 
The forms figured by Wiihner in his “Unteren Lias”* may be divided into 
three subseries. It was not practicable to determine whether these series were 
artificial or natural, though many figures of the young were given by Wihner. 
The first series can be distinguished by the finer pila and somewhat com- 
pressed whorls. They are as follows. Schlot. catenaia, Wih., and angulata, in the 
Planorbis bed. The following, though still discoidal, are slightly more involute 
forms, if one can say this after comparison with Neumayr’s figure of angulatum 
from Pfonsjoch? They are Schlot. montana, Wiah., Plates XIX., XX., Donar, Plates 
XIX., XXL, eatranodosa, Plate XX., pachygaster, Plate XXI, and marmorea, Plate 
XXIL, and all occur in the Megastoma and Marmorea beds. 
The second or coarsely pilated series have more gibbous forms in the young 
and much deeper channels, or, in other words, the piles have more prominent ter- 
minations on the abdomen. The discoidal forms are as follows. Schiot. ind., Plate 
XVUI. Fig. 4, which has in an exaggerated condition the characteristics of the 
subseries, and may be a pathological specimen, fawrina, Plate XIX. Fig. 5, angu- 
lata, var. ind., Plate XX. Fig. 5. All three of these were found in the Megastoma 
and Marmorea beds, but were followed by two young forms occurring, according 
to Wihner, in the Rotiformis beds. These are Sehlot. scolioptycha and posttaurina, 
Plate XXIII, and appear to have been the young of species, which may have 
been more involute in the adults. 
The third subseries has young with even stouter whorls than in the second 
subseries, though not otherwise separable. Schiot. trapezoidale, the first species, 
occurred, according to Wihner, in the Marmorea bed, and was succeeded by 
ventricosa, Plate XXIII., and an undetermined form, Plate XXII. Fig. 12, both 
in the Rotiformis bed. 
Canavari in “ Unteren Lias von Spezia” describes dwarfs or young of Schist. 
(Aigoc.) trapezoidale, Plate XVIL. Fig. 8, 9, and ventricosum, Plate XVII. Fig. 10, 
which seem to be identical with forms described by Wiihner ; also Schiot. (-Aigoc.) 
catenatum, Fig. 1, comptum, Fig. 3-5, Collegnoi, Fig. 6, all of which are very closely 
allied, and may be either young or dwarfs of Schiot. Charmassei, or the more invo- 
lute varieties of Schlot. angulata. 
Srconp SUBSERIES. 
The abdominal channel is narrower and deeper proportionally than in the 
first subseries, and is a true furrow, in place of being a smooth zone or mere 
depression formed between the interrupted pils, as in Weehneroceras and in the 
first subseries of Schlotheimia. The shells known are finely pilated, and the 
furrow is similar to what it is in the young of some species of the first subseries.° 
The species have been found only above the Bucklandi zone, and are all, so far 
as known, dwarfs. 
1 Mojsis. et Neum., Beitr., [V., 1886. 2 Abh. k. k. geol. Reichsans., VII., pl. ii. fig. 5. 
8 See Schlot. trapezoidale, Wih., Mojsis.-et Neum., Beitr., IV. pl. xxiii. fig. 2c, and others on the same 
plate. ; 
i — einem 
ST atten 
