314 ME. s. s. BrcKMA:N' o:s [vol. Ixxiii^ 



not a non-sequence due to lack of iurneri beds, for the species 

 cited by Wright as A. honnardii is possible evidence for them. 



The true hirchi beds were presumably present — on the supposi- 

 tion that Wright was referring to the true hirchi or a very near 

 form, and not to 2Iicrocleroceras sepiigerum, when he says 'I have 

 several specimens [of ^goceras birchii~\ which were collected from 

 the railway-cutting near Bredon.' ^ 



The evidence for an Arnioceras fauna being there and occurring 

 in a chalky matrix has alread}^ been given ; the same details refer 

 to Agassiceras, see above, p. 312, to which may be added that 

 Wright figures a large Agassiceras from Bredon.- 



Lymian. — Arnioceras is in the main a genus easy to recognize 

 from other Arietidse. with its straight sharp ribs and smooth inner 

 whorls : the onh' difficult}^ i^i^J be with body-chamber fragments. 

 But the species of Arnioceras are numerous and not easy to 

 separate ; yet for the detailed work now required such recognition 

 will be necessary, in order to see what the succession of species is 

 in time. Old records, where the various species of Arnioceras are 

 just cited as Ammonites semicostatus without further distinction, 

 serve but a limited, and it ma}^ be a somewhat misleading, purpose. 

 For there is reason now to be sceptical whether the placing as 

 isochronous of semicostatus beds — that is beds containing Arnio- 

 cerata — is really correct. Faunal repetition and non-sequences 

 may have been overlooked. 



Of the species now figured the characters ai-e sufficiently obvious : 

 Arnioceras jiavum is a carinate smooth form, A. anageneticum 

 shows the beginning of ribs, A. fortunatumh almost wholly ribbed,, 

 distinguished by its markedly-reclinate somewhat distant costae. 



Thirteen species oi Arnioceras are enumerated from the Whitby 

 district of Yorkshire, -^ and (speaking from memor}") all of them are 

 more or less distinct from the species now figured. In Lincoln - 

 shii-e there is a rather heavy form with strong ribs usually called 

 Ammonites geometricus Oppel, if and when distinguished from 

 A. semicostatus. There may be more than one species involved; 

 but the shells are of very distinct character. This form (or these 

 forms) are constant among all series of Lincolnshire Lower Lias 

 ammonites ; but from other British localities they are lacking, or 

 only occur exceptionally. 



From the Cheltenham district Arnioceras hodleyi seems to be 

 the special form ; it is not quoted from Yorkshire in the list cited 

 above ; it occurs in Wiirtemberg, but can hardly be usual there, 

 for onh^ a poor fragment is figured by Quenstedt, see p. 302. 



Arnioceras fortiinatiim is known to me at present only from. 



^ Proc. Cottesw'old Nat. F. C. vol. iii (1864) p. 179, repeated in ' Monogr. 

 Lias Ammonites ' 1882, p. 333 ; and see below, (e) p. 319. 



- Proc Cotteswold Nat. F. C. vol. iii (1861) pi. ii, fig. 1, refigured in ' Monogr, 

 Lias Ammonites' 1878, pi. viii, figs. 1, 2, Arietifes sauzeanus : below,, 

 (e) p. 321. 



3 ' Geol. Whitby' 2nd ed. Mem. Geol. Surv. 1915, p. 98. 



