446 MR. 8. S. BUCKMAN ON THE GROUPING OF SOME [Aug. 1 898, 



series.^ Caloceras ^ must be removed from the Arietidse on account 

 of its septation ; and because of this very character it forms vp'ith 

 the genera Psiloceras, WcEhneroceras, and Schlotheimia a well-marked 

 family, Psiloceratidge, which flourished during the Caloceratan Age 

 (time of Hettangian Stage) and almost completely came to an end 

 in the hem era marmorece. 



As to the exact connexion of this family with the particularly 

 Triassic ammonites there is at present considerable doubt. In out- 

 ward form they seem to be near many of them ; but outward form 

 in ammonite-classification and genealogy cannot be trusted, though 

 Mojsisovics gives us only this and too few suture-lines upon which 

 to form opinions. Then there is a great paucity of described species 

 from the Ehaetic^ and from the underlying beds of the zone of 

 Sirenites Argonautce. As to the ammonites of this zone, Mojsisovics 

 saj'S that most of them are undeterminable owing to their bad 

 preservation. But upon a consideration of the ammonite-fauna I 

 venture to say that the Caloceratan Age should be regarded as the 

 close of the ' Triassic ' Period ; that there is at the close of the 

 Caloceratan Age quite a new departure in regard to the ammonite- 

 fauna — an incursion of a new series, which, forming two families, 

 Arietidse and Hildoceratidae, holds dominant sway throughout the 

 Arietidan Epoch (time of Eojurassic Series) ; and that the greatest 

 faunal break between the ' Triassic ' and ' Jurassic ' Periods occurs 

 at this date, when the Psiloceratidae give place to the ArietidiB. 



As to the sedimentary change which occurred towards the end of 

 the ' Triassic ' Period, I wish to protest against the assumption of 

 its contemporaneity. The argument for such an assumption usually 

 travels in a circle — that the change of sediment marks the close of 

 the Trias, therefore, i/pso facto, wherever the change occurs is the 

 close of the Trias, because of the change; and so the inference is 

 that the sedimentary change was contemporaneous. But this takes 

 for granted the very point which has to be proved, namely, that the 

 change was contemporaneous ; and the only proof of such contem- 

 poraneity can be given by palaeontology. 



Even if the contemporaneity of the change were proved, it need 

 not affect the biological aspect of the case, which is that the 



^ The foUoTiving species belong to Bayle's genus Eckioceras : — raricostatum, 

 d'Orb., the type ; Patti, Dumortier; Bodleyi, Dum. {non J. Buckm.) ; armen- 

 tale, 'D\im.{ FauU, Dum.; Oosteri, Dum.; tardecrescens, Dnm. (?i07i Hauer) ; 

 jejunum, Dum.; viticola, Dum.; Edmundi, Dum.; vellicatmn, Dura.; Nodo- 

 tianum, d'Orb. ; Macdonelli, Portlock ; aplanatum, Hyatt ; and, somewhat 

 doubtfully, carusense, d'Orb. ; Kewherryi, Hyatt ; ceduense, Dum. 



^ Many of the species of Caloceras are figured by Wahner from the marmorea- 

 beds of the North -eastern Alps, and the same peculiarity of septation is notice- 

 able in them — the dependent, obliquely-directed inner lobes ; see ' Beitr. tieferen 

 Zonen d. unt. Lias in d. nordostl. Alpen,' Pal. Oesterreich-Ungarns. 



^ I fully anticipate that the results of future work will show that the beds 

 now called Rhsetic are not strictly contemporaneous deposits, but that the 

 case will prove similar to that of the ' Midford Sands ' in connexion with Lias 

 and Oolite respectively — namely, that what is Lias in one place is called 

 Bhaetic elsewhere, and what again is E ha tic in another place is called 

 Juvavische Stufe somewhere else. 



