344 Viscount d'ARCHiAC and M. de Verneuil's 



1. Orthoceratites regularis, Schlot. Die Petrefact., p. 54. O. recto, Bosc. Conchyl. ; O.reff., he'iDechen 

 Handb. der Geogn. von De la Beche, p. 535 ; Kldden, Die Verstein. Mark Brandenburg, pp. 131, 31 1 ; 

 Holl, Petref., p. 235. O. CEkmdiciis, Knorr, Recueil des Monum. Tome II. PI. II, I.* f. 8 ; Tome IV. 

 Suppl., PI. IV. e, f. 1-5, and PI. V. d.f.2; Breyn, Opuscula PI. III. f. 1, 2, 5, 6 ; Bronn, Leth. geog., 

 PI. I. f. 10; His. Leth. Suec, PI. IX. f. 3; Miinster, Beitr. z. Petrefact., Heft iii. PI. XVII. f. 3, 4. 

 Variety Tab. nost. XXVII. f. 2. 



Shell smooth, of a very elongated cone shape, septa very distant, horizontal, subhemispherical ; siphon 

 small, quite central and discontinuous according to Count Miinster, each little tube only extending 

 a fourth of the depth of the chamber. 



Bronn says, that specimens are found which are slightly and irregularly striated transversely, and 

 others which are smooth at the anterior part and encircled at the summit by little transverse ridges. We 

 have observed that some individuals which present this latter character, belong to another species whose 

 siphon is marginal. 



The O. regularis, as may be seen by the numerous synonyms, has often been described and figured ; 

 nevertheless upon comparing the figures and the descriptions of various authors it will appear that there 

 is still much uncertainty with regard to it, at least as to certain characters. According to Count Miinster 

 the diameter of the septa is equal to half the height of the chambers ; and upon consulting his figure we 

 find that at the anterior part the diameter is equal to the height of two chambers, while toward the 

 summit it is only equal to two-thirds of one chamber. In the Lethma geognostica the diameter of the 

 septa is to the height of the chambers sometimes as 1 to 4, sometimes as 1 to 3, or only 2 ; and this last 

 relation is not presented at the apical part, but, on the contrary, toward the middle. It is just the same 

 with Hisinger's, where this relation is nearly as 1 to 4. 



Our specimens from the slates of Wissenbach differ from these various proportions and also from all 

 the species we are acquainted with in the great altitude of the chambers, which is at least equal to the 

 diameter of the septa, and sometimes even beyond that, as in the specimen which we have represented. 

 In all the other details these shells are like O. regularis. 



The relation between the diameter of the septa and the height of the chambers appears to be a cha- 

 racter of no importance ; this proportion varies with age ; and the chambers are proportionally lower as 

 they are more distant from the summit of the shell, or as they are more newly formed. Still this rela- 

 tion is not exact between two shells of the same diameter which we might suppose to be of th^ same age : 

 in fact we shall see in O. triangularis chambers of unequal altitudes alternating without any regularity. 



In the same beds we meet with little parcels or bundles of acicular Orthoceratites from 7 to 8 milli- 

 metres in length by half a millimetre in width. These microscopic shells, which are always slightly 

 curved, appear to be the young of the Orthoceratites regularis, although we have not always been able 

 to ascertain the place of the siphon. The greater number of them are smooth, but there are some also 

 which are finely annulated ; and as it is reasonable to suppose that all the individuals of one bundle belong 

 to the same species, of which they would be the gemma, these external differences might be thought 

 to be characteristic of the sexes of the individuals. 



Wissenbach, CEland, Elbersreuth, Schiibelhammer, Prague, Revel, West Gottland ; forming rolled 

 pebbles in the Mark Brandenburgh, &c. 



2. Orthoceratites gracilis, Blum., Arch. Telluris, Pi. II. f. 6. De la Beche, Trad. Franc, p. 556. Tab. 



nost., XXVII. f. 4. 

 Shell in form of an elongated cone. Septa numerous, horizontal, subhemispherical. Siphon small, 



rounded, placed at an equal distance from the centre and the edge. Toward the middle part of the 



shell the diameter of the septa is equal to the height of two chambers. 

 This species differs from the preceding in the number of its septa, which is at least double ; in the 



