part 4] jUEASSic cheonologt : lias. ' 311 



and quite a considerable number in the former which require investi- 

 gation : they do not necessarily belong to the present genera. In 

 fact, the Oxynotoids appear to represent the catagenetic terminals 

 of man}^ different lineages, of which the majority came into view 

 suddenly in the European Deiran without an};^ ancestry. Only 

 Ammonites oxynotus Quenstedt, and A. oxynotus Dumortier, two 

 quite different species, seem to have traceable ancestors — the former 

 beino- connected with a tuberculate ^ and the latter with Arietites 

 of t\\ii fowleri-colleiiottii pattern. ^ 



The placing of the Radstock Ox3aiotoid fauna later than the 

 Grloucestershire one {Gleviceras) is a surmise not yet proved; but 

 their difference in species shows that they are distinct in date. 

 To place the Eadstock fauna before the Grloucestershire one would 

 involve the supposition of another non-sequence in Grloucester- 

 shire.*'^ Gleviceras belongs to a distinctl}^ higher horizon than the 

 oxynotum beds in Glloucestershire ; but, if that were not known, 

 the absence of Gleviceras from Wiirtemberg, where A. oxynotus is 

 conspicuous, would be presumptive evidence of a difference of date. 



It is notable that no specimens of the Radstock Oxynotoid fauna 

 are figured by Quenstedt, and only two examples wdiich have the 

 aspect of constituents of the Gleviceras fauna — Ammonites gui- 

 halianus Quenstedt, 'Ammoniten d. Schwabischen Jura' pi. xxviii, 

 figs. 3 & 4 — not from an}^ oxynotus locality, and from a higher 

 horizon (Lias y). Pompeckj has named them Oxynoticeras 

 joaradoxum, and places them m jamesoni \leckenhyi?~\ zone. They 

 have neither suture-line nor ribbing of Gleviceras ; and not the 

 ribbing of Guihaliceras. Present experience would suggest that 

 their position may be due to derivation. 



Mercian-Lymian. — The Barrow Gurney fauna {Arietites 

 turyescens, p. 296, and Microderoceras injlatum, p. 305) is con- 

 gruous with that of Bredon (Worcestershire), certainly as regards 

 the Arietites and presumably with regard to the Microderoceras 

 (see below, p. 312). But this special fauna is not known from 

 intermediate areas, is absent from Dorset and also from Yorkshire 

 so far as my experience goes. Dumortier shows a partly com- 

 parable Microderoceras fauna, but not Arietites ; Re3mes shows 

 Arietites, but not any Microderoceras of the style required.* 

 Quenstedt shows nothing comparable.-^ A first inference ma}^ 



^ See ' Yorkshire Type Ammonites ' i (1909) p. 7 b. 



^ To these may now be added Gleviceras, see above, p. 292. 



3 See p. 272. 



^ ButReynes is unsafe: his specimens are from many areas ; and see p. 322. 



' One can in the main only go by what is published. I know from my own 

 and other collections that a great mass of new material is unpublished. I 

 write with some knowledge of that, although memory necessarily has its limi- 

 tations in this respect, owing to the difficulty of fixing new forms in one's mind 

 because of their lack of names. Even photographs help little without names 

 to serve as tags for the memory. But, if similar conditions obtain on the 

 Continent, then of course the statements made above might be invalidated. 

 On the other hand, Continental Ammonitology is far more complete in many 

 areas than is the British. 



