part 1] juhassic chkonologt : lias. 99 



Table XIII. — Revised Chronology. 



Age. 



Former paper. 





Suggested divisions. 



Whitbian 



7. subcarinata. 



7 b. 



bifrons. 







7 a. 



subcarinata. 





4. exaratum. 



4 b. 



exaratum. 







4 a. 



murleyi (Fish-Bed). 1 





2. acutum. 



2 b. 



acutum. 







2 a. 



athleticum. 



RAASAYAN 



7. leckenbyi. 



7 b. 



leckenbyi. 







7 a. 



lorioli. 





4. raricostatoides. 



4 c. 



raricostatoides. 







4 b. 



tubellum. 







4 a. 



rhodanicum. 





3. bispinigerum. 



3 b. 



2nd armatoid. 







3 a. 



bispinigerum. 





2. subplanicosta 



2 b. 



subplanicosta. 





(densinodumj . 



2 a. 



obsoletum (densinodumj. 





1. 1st Echioceras. 



lb. 



1st armatoid. 







la. 



1st Echioceras. 



Mercian 



7. denotatus. 



7 c. 



lacunata. 







7 b. 



subpolita. 







7 a. 



denotatus. 



These subdivisions are not to be regarded as foregone conclusions. 

 They are in some cases theoretical, based mainly on evidence of 

 geographical discrepancies in distribution shown in the paper, and 

 they are put forward with the distinct intention of inciting further 

 research. 



And it is not to be concluded that they are final, either as 

 regards the number of divisions or as to the names appended. For 

 instance, Raasayan 4 will probably require still further division : 

 see Table VII, p. 79, of this paper, and see also for additional 

 evidence my ' Pakeontologieal Classification ... of certain Jurassic 

 Rocks of Skye & Raasay,' Table iii, p. 70 ('The Mesozoic Rocks 

 of Applecross, Raasay, & North-East Skye ' Mem. Geol. Surv. 

 Scotland, 1920). A necessary prelude to such further division is 

 a critical examination and adequate illustration of the very numerous 

 series of Echiocerata — a task of considerable magnitude. When 

 that is completed, it may be found that other names than those 

 now selected are more suitable for marking the Echiocerate 

 horizons ; the same may be the case in regard to other divisional 

 names : too often they have to be used on the principle of ' that 

 or none.' 



(10) The analysis of the Gloucestershire Lias described by 



1 The lower part of the latescens zone of B. Thompson (' Geology of North- 

 amptonshire ' Geol. Assoc. Jubilee vol. 1910, pp. 462, 463), containing carinate 

 serpenticones of latescens aspect ; but A. latescens Simpson is a Pseudo- 

 grammoceras of Yeovilian 4 (see II, 4, No. 79). Such carinate serpenticones 

 from the Fish-Bed of Alderton-Dumbleton (Gloucestershire) had been named 

 A. murleyi by my father (I, p. 90), which I always thought was a nomen 

 nudum. But lately, thanks to Mr. J. W. Tutcher's bibliophile ardour, dis- 

 covery of figure and description has been made in a copy of Moxon (XI, 

 pi. xxiv, fig. 6, and explanation of the plate) — now a scarce work. 



