112 GENESIS OF THE ARIETIDA. 
Rhone. The last two are closely comparable in aspect with species figured by 
Hauer from the Adneth limestones.’ In the same way, we should be disposed 
to regard the Mediterranean province as the autochthonous home of some genera 
of the Middle Lias, which appear here in association with the Arietide. 
The Arietide afford an excellent standard, since their genera and species 
have been found, with rare exceptions, only in the Lower Lias; and, so far as 
our knowledge now goes, the series of forms and cycles have a very complete 
and satisfactory aspect, indicating a history of progress and decline within the 
limits of that group of strata in the faunas of Central Europe. 
In the Mediterranean faunas, however, so far as known, only the rise of the 
group is recorded in the sediments and fossil remains, and its acme and decline 
are not clearly indicated. We have been accustomed to look upon the fauna of 
the Hierlatz beds as composed for the most part of degraded dwarfs, whose pecu- 
harities or modifications were due to the unfavorable action of the surroundings 
upon migrants from other contemporaneous faunas of the Lower Lias. This 
seems to be the only theory which can account for the prevalent smaller size 
and more or less degraded aspect of many of the shells, when compared with 
their nearest allies in other locations. 
SUMMARY. 
The facts cited above, though far from complete, show that the series of the 
Radical and Plicatus Stocks, with the exception of the vermiceran series, were 
probably evolved in the Mediterranean province. The series of the Levis Stock 
had however a different history, since they probably arose in the basins of Cen- 
tral Europe. We therefore venture to differ in part from the eminent geologist 
and paleontologist Neumayr, who regards, if we properly understand his views, 
the Northeastern Alps as the aldainic home of the whole of the Arietide. 
The sutures of all the Mediterranean forms of Psiloceras and Caloceras are, as 
figured by Wihner, more complicated, or, as we should say, more triassic than 
those commonly found in Central Europe; but we occasionally find a variety of 
Psil. planorbe, like that figured by Quenstedt? and by Wright,’ in which there is 
a close approximation to the outlines common in the Mediterranean province. 
After having written the above, we were extremely gratified to find precisely the 
same results with regard to the relation of caliphyllum and planorbe, but more fully 
and exactly stated by Neumayr, in his “ Unterster Lias” (p. 25). His conclu- 
sion, that planorbe is consequently a derivative of Psil. caliphyllum, and is char- 
acteristic of Central Kurope, while the latter species is equally characteristic of 
the Mediterranean province, is sustained by the fact that the sutures of caliphyl- 
1 The peculiarities of the senile whorls are similar to those of Oxynoticeras Lotharingum, and will lead 
to much confusion until the sutures and the young are fully known. It is quite possible that our own con- 
clusion may be wrong in this respect, but the sutures of Salisburgensis and altus, Hauer, are Lytoceran, and 
the aspect of these compressed shells is very similar to that of those found in France, whose sutures are 
however unknown. The young are known only in Driani, which resembles some of the forms described 
by Herbich. 
2 Amm. d. Schwab. Jura, pl. i. fig. 19. 8 Lias Amm., pl. xiv. fig. 1, 
te 
