PSILOCERAS AND CALOCEEAS. 89 



advantages attending residence at a distance from the fields of research, the 

 results have appeared to be sufficiently novel and suggestive to warrant publica- 

 tion. The results reached have been just what one might have anticipated from 

 a •priori reasoning upon the basis of the theory of evolution and monogenesis, 

 but nevertheless have not been admitted without much hesitation, because of the 

 author's natural feeling that so great exactitude in statement with regard to the 

 relative age of faunas on the same horizon should be distrusted. 



If our data have led us correctly, there are some basins in the Lower Lias 

 which were capable of evolving new forms. These we have called Aldainic 1 

 Basins, because they were centres of origin for new series, and their faunas were 

 what we have called Autochthonous Faunas. Other basins were apparently 

 incapable of giving origin to new forms, or at any rate received all, or almost 

 all, the forms which occupied their territory by migration from the aldainic basins. 

 These we have called Analdainic or Residual Basins, and their faunas Residual 

 or Analdainic Faunas. The beginning of the Arietidae was in the Northeast- 

 ern Alps, and this, being the first autochthonous fauna, was older than all others. 

 Thence South Germany or Suabia was peopled by chorological migration, and 

 then the basin of the Cote d'Or. Thus a Zone of Autochthones, or an aldainic 

 band of basins, was formed running to the westward. North and south of this 

 zone all faunas seem to have been residual faunas. 



The fauna of the Lower Lias in the basin of the Northeastern Alps was, how- 

 ever, not in the zone of autochthones after the deposition of the Angulatus bed. 

 This zone, just before the deposition of the Lower Bucklandi bed, had become 

 narrowed in its easterly extension, and confined to the faunas of South Germany 

 and the Cote d'Or. 



PSILOCERAS AND CaLOCERAS. 



The discovery by Giimbel 2 of Psil planorboides in the triassic strata of the 

 Bavarian Alps having been confirmed by Winkler 3 and the shell and sutures 

 figured, there can be no doubt that it is a true Psiloceras. As a result of our 

 researches upon cycles of form, we can, however, unhesitatingly assume that this 

 shell is too involute to be considered a radical of the Arietidse. It indicates, if 

 estimated according to the usual history of these cycles, that undiscovered species 

 of discoidal Psiloceratites must have existed in the Trias, as necessary antece- 

 dent or ancestral forms. Two forms have also been cited by Neumayr, in his 

 " Unterster Lias," 4 as JSffoe. planorloides and JEgoc. form. nov. from the Kossener 

 shales. These are from Wallegg, and appear to be the same as those previously 

 cited by Stur 5 as Amm. cf. hngipontiniis and later described by Wahner. 6 Wah- 

 ner considers them both to be specimens of his Psil. Rahana, and writes that 



i 'AXSmVco, to make to grow. 2 Ober. Abth. d. Keupers, p. 410. 



* Zeits. deutsch. geol. Gesellsoh., 1861, XIII. p. 489, pi. ix. fig. 3. Neumayr also, Unterster Lias, 

 Abhand. geol. Reichsans., VII., figures this species in the Planorbis bed. 



4 Abh. geol. Reichsans., Wien, VII. p. 44. 



5 Fuhrer z. d. Excursion, d. deutsch. geol. Gesellsch., Wien, 1877, p. 148. 



6 Verhand. geol. Reichsans., 1886, p. 175. 



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