92 GENESIS OF THE ARIETID.E. 



In North Germany, according to Schlonbach, 1 the Planorbis horizon is pres- 

 ent ; but Psil. planorbe is largely, if not entirely, replaced by Cal. Johnstorri, and he 

 designates this layer as the "zone of Amm. Johnstoni." Braun 2 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 Johnstoni was abundant, and of large size. Rb'mer, 3 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 Tentoburger Waldes bei Altenkirchen," shows that a thick 

 Planorbis bed occurs in this locality, and Psil. planorbe is abundant, while Cal. 

 Johnstoni, which he considers to be identical with planorbis, var. plicata, and Amm. 

 hqueolus, is much less frequent. 4 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. 5 



The paleozoological 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 Gotham 6 are found side 

 by side. This was also the richest collection in calocerau 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 Johnstoni, which 

 is probably the Caloceras bed. Wright's section at Uphill railroad cutting shows 

 the bed containing " angulatus and fragments of Liasicus," called by him the 

 " Angulatus bed," and at Binton, Warwickshire, there is a transition bed con- 

 taining only Liasicus, included by him in the Planorbis zone. 7 In his sections of 

 the Planorbis horizon Psil. 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 Risen, rl. Mittl. Lias, etc., Zeits. d. geol. Gesell., 1863, p. 498; Paleontogr , XIII.; and Die 

 Ilannoverische Jura, p. 17. 



- Her utitere Jura in nordwestliche Deutschland, 1871. 



3 VersU'in. norddeutsch. ool. Geb. 



4 Zeits. deutsch. geol. Gesellsch., 1866, XVIII. p. 40. 

 6 Amm. Schwab. Jura, pi. i. fig. 17. 



6 Stoddart, in bis " Notes on the Lower Lias of Bristol," Geol. Mag., V., 1868, p. 139, shows that Amm. 

 Johnstoni occurs 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. 



