116 GENESIS OF THE ARIETID. 
Spezia, and another higher horizon, which is supposed to be the equivalent of the 
Bucklandi horizon. This last is said to contain Cephalopods representing all the 
later faunas of the Lower Lias, and some species are quoted as being referable to 
the Middle Lias, 
Canavari, in his ‘‘ Fauna der unteren Lias von Spezia,” so frequently quoted 
above, states that the fossils occur in a single zone, which does not admit of sub- 
division, though it was carefully investigated, layer by layer, by Cocchi. He 
states also, that it is unquestionably the lowest of the lower lias sediments in 
Italy, and comprises all the horizons except those of Planorbis and Oxynotus. 
He considers that the fossils have closer affinities with those of the Mediterranean 
province than with those of Central Europe, a fact which seems to be established. 
The species of the Lytoceratide and of Amaltheus, ete. which are supposed 
to be anachronic and to indicate a fauna derived from the Middle and Upper 
Lias, appear to us to be found in their appropriate positions, like those of the 
Northeastern Alps. They may be either the radicals of the similar forms which 
oceur in the Middle and Upper Lias of the Central European faunas, or morpho- 
logical equivalents, or pathological specimens.! This is also Canavari’s opinion 
with relation to some forms, since he expressly states that the agoceran species, } 
| as he calls them, are the immediate forerunners of Microderoceras. The fauna 
i of the Rhone basin is almost exclusively composed of species having a Central 
European aspect. There are, it is true, some slight indications, in the presence 
of three species of Lytoceratidee in this basin, that the migrants may have come 
this way on their march into Central Europe, but there are no supporting facts 
with which we are acquainted. The absence of the Planorbis horizon, or at any 
rate its sporadic appearance in Italy, and the absence of Ammonitine in this 
horizon of southern Provence, are very serious difficulties in the path of a sup- 
posed southern track of migration. 
The evidence, so far as known, seems therefore strongly in favor of the view, 
that during the time of Planorbis and Caloceras, and perhaps earlier in the 
Angulatus horizons, the stream of migration flowed south and westerly from the 
Northeastern Alps into Italy, while another from the same basin directed itself 
westerly along the then existing coast lines into the basins of South Germany | 
and the Cote d’Or, and the species were distributed thence into the basins to 
the north and south of these two, in the province of Central Europe. In South 
Germany and the Cote d’Or the conditions became favorable during the time of 
the Angulatus horizon for the evolution of Vermiceras among the descendants of 
the Plicatus Stock, and for the origin of Coroniceras, Arnioceras, and Agassiceras 
of the Levis Stock. Asteroceras arose later in these same faunas in the Upper 
Bucklandi beds, and Oxynoticeras probably even still later, though here the 
series is evidently older than the date of its first appearance. The migrations of 
i these genera spread the forms to the east into the faunas of the Northeastern 
1 The figures of Amaltheus given by Canavari in his last work, “‘ Fauna del Lias inf. della Spezia, 
R. Comit. Geol. d’ Italia,” III., Pt. II. pl. vi. are certainly startlingly similar to Amaltheus, but such 
resemblances in forms of widely distinct series are not uncommon. See the pathological case figured on 
Plate X. Fig. 19 of this memoir, and others quoted in the descriptions of the species. 
