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92 GENESIS OF THE ARIETID. 
In North Germany, according to Schlénbach,' the Planorbis horizon is pres- 
ent; but Psil. planorte is largely, if not entirely, replaced by Cal. Johnstoni, and he 
designates this layer as the “zone of Amm. Johnstom.” Braun’ gives similar 
results for his work in the localities of northwestern Germany; and Emerson, 
in his essay “ Die Liasmulde von Markoldendorf,” did not find Psiloceras in that 
basin, though Johnstow was abundant, and of large size. Romer,’ the first ob- 
server in North Germany, states that the Lower Lias is less developed in that 
region than in South Germany, and enumerates only a few species. Schliiter, in 
his “Schichten des Teutoburger Waldes bei Altenkirchen,” shows that a thick 
Planorbis bed occurs in this locality, and Psi. planorbe is abundant, while Cad. 
Johnstoni, which he considers to be identical with planorbis, var. plicata, and Amm. 
luqueolus, is much less frequent.t He also gives Amm. angulatus as appearing in 
the upper part of the same bed. There is unfortunately no record of the exact 
beds in which the fossils occurred, and it is not certain, therefore, whether we are 
here dealing with the Caloceras bed or a true Planorbis bed. Quenstedt also 
describes and figures a specimen of Psil. planorbe, var. leve, from Quedlinburg.? 
The paleozodlogical and geological data, therefore, appear to sustain the 
conclusion, that Psiloceras and Caloceras, as a rule, arrived later in North Ger- 
many and Luxemburg, the Cote d’Or, and the Basin of the Rhone, than in 
South Germany. 
In England the aspect of the fauna has greater similarity with the Cote d’Or 
and South Germany, than with the North German and Luxemburg basins. The 
Planorbis zone is well developed, and in the Bristol Museum the South German 
varieties of Psil. planorbe and the English forms from Cotham® are found side 
by side. This was also the richest collection in caloceran species which we saw 
in England, though it was still far behind that at Semur. Rev. J. E. Cross, in 
his “ Geology of Northwestern Lincolnshire,” claims that no true Planorbis bed 
occurs, but in place of this a bed containing Amm. angulatus and Johnston, which 
is probably the Caloceras bed. Wright’s section at Uphill railroad cutting shows 
the bed containing “ angulatus and fragments of Laasicus,” called by him the 
“ Angulatus bed,’ and at Binton, Warwickshire, there is a transition bed con- 
taining only Zvasicus, included by him in the Planorbis zone.” In his sections of 
the Planorbis horizon Psd. planorbe occurs earlier than any species of Caloceras at 
the Uphill railroad cutting; at Binton, Warwickshire ; Street, Somerset ; and at 
Brockeridge and Defford Commons. No mention, however, of Psiloceras in any 
earlier bed occurs, and its appearance must therefore have been later, as a rule, 
1 Ueber Eisen. d. Mittl. Lias, etce., Zeits. d. geol. Gesell., 1868, p. 498; Paleontogr., XIII.; and Die 
Hannoverische Jura, p. 17. 
2 Der untere Jura in nordwestliche Deutschland, 1871. 
8 Verstein. norddeutsch. ool. Geb. 
4 Zeits. deutsch. geol. Gesellsch., 1866, XVIII. p. 40. 
5 Amm. Schwab. Jura, pl. i. fig. 17. 
6 Stoddart, in his “ Notes on the Lower Lias of Bristol,” Geol. Mag., V., 1868, p. 139, shows that Amm. 
Johnstoni oceurs in the section he described earlier than true planorbis, if one can judge from the names he 
gave to the beds, since no lists of fossils were added. ‘The section given certainly indicates the existence of 
a Caloceras, rather than a true Planorbis bed. 
7 Wright, Lias Amm., pp. 11, 20. 
