PSILOCERAS AND CALOCERAS. 91 



M. Collenot 1 mentions Amm. Johnstoni, tortilis, laqueiim, and Burgundies as oc- 

 curring in the Planorbis horizon. The collections at Semur show that Planorbis 

 was small, and evidently already losing ground, whereas the fine suites of calo- 

 ceran fossils indicate at least that this series had suffered no loss by migration 

 when compared with the fauna of South Germany. This collection is also 

 arranged to show a bed similar to the Laqueum layer of Quenstedt, called by 

 Collenot the " zone of Amm. Liasicus," which contains only caloceran forms, and 

 also Psil. longipontinum. Cal. laqueum is smaller, and more like the German form 

 when found in company with Liasicus? A few dwarfed forms of Psil. planorhe, 

 var. leve, have been found together at Saulieu, and at Beauregard there is a bed 

 with large forms of Cal. Johnstoni and tortile, accompanied by a larger form of Cal. 

 laqueum than is usual in South Germany, and a small Psil. planorhe, var. leve. The 

 latter is in Boucault's collection, Museum of Comparative Zoology, but not rep- 

 resented at the time of my visit in the collections at the Museum of Semur. The 

 researches of M. F. Cuvier 3 are important in this connection. He states that a 

 separable Planorbis bed was found by him on the section of the railway between 

 Arcy-sur-Cure and Guillon, and immediately above this a bed characterized by 

 the presence of Cal. Liasicum. Again, on page 177, he speaks of finding at 

 Gravelles, near Saulieu, a bed containing Psil. planorhe and Cal. laqueum or Bur- 

 gundim, and this agrees with Collenot's observations. 



Dumortier 4 states that Psil. planorhe occurs everywhere in the Planorbis bed 

 of the basin of the Rhone in company with Cal. Johnstoni, though not an abun- 

 dant fossil, and from a fragment in his possession infers that the former may in 

 some cases have reached the great diameter of 220 mm. Quenstedt describes and 

 figures a specimen of Psil. planorhe, var. leve, from Provence, 5 which he names Amm. 

 psilonotus provincialis. Martin 6 designates the Planorbis bed in the region of the 

 Cote d'Or as the " zone of Amm. Burgundies" (our Cal. laqueum). He considers 

 that the beds of " lumachelle," the Planorbis horizon, show evidences of having 

 been deposited during a period of violent currents, etc. This is an important 

 fact, since it indicates the littoral character of the deposits. 



Terquem, 7 in the department of Moselle, writes that Ammonites are generally 

 rarer and more often broken than Nautili in the Lower Lias, and enumerates 

 only six species. Chapuis and Dewalque state 8 that in Luxemburg the Planor- 

 bis zone is not fossiliferous. 9 



1 Description Geologique de l'Auxois, p. 209. 



2 The remarks of M. Collenot on page 164 are very instructive, and confirm the impressions received 

 from the collections at Semur. 



s Notice Geologique, etc., Bull. Soc. de Semur, ser. 2, No. 3, 1S86, pp. 170, 176. 

 4 Etude Paleontologique du Bassin du Rhone, p. 28, pi. i. 

 6 Amm. Schwab. Jura, pi. i. fig. 19. 



6 Pal. Strat. de l'Infra-Lias de la C6te d'Or, Mem. Soc. Geol. de France, VII. 



' Infra-Lias Luxem., etc., Dept. Moselle, Mem. Soc. Geol. France, V. See also, for similar opinions, 

 Collenot, Descr. Geol. de l'Aux., p. 162, and Dumortier, Etudes Pal. Bass, du Rhone, I. p. 20, II p. 97. 



8 Descr. Foss. Terr. Secon. de Luxembourg. 



9 The late researches of Schumacher, Steinmann, and Van Werveke, Erlaut. z. Geol. Uebersichtsk. d. 

 Westl. Deutsch-Lothringen, show that the Planorbis bed containing Psil. planorhe, var. plicatus, is found in 

 the region explored by them, though it is absent in the French part of Lothringen, as stated by Bleicher, 

 Bull. Soc. Geol. de France, ser. 3, XII., 1884, p. 445. In Deutsch-Lothringen it is one meter in thickness. 



