parti] JURASSIC CHRONOLOGY : LIAS. 71 



decidedly against that conclusion. The ammonites contempora- 

 neous with the hrachiopods would, on the theory now propounded, 

 have occupied areas farther in on the Continental shelf ; and these 

 ammonite-deposits made in such areas may have heen destroyed by 

 successive later erosions when these areas were raised, coincidently 

 with the shallowing of the western sea, after the brachiopod 

 interludes. The hrachiopods themselves lend some support to a 

 deep-sea theory — ffliynclionella thalia is a comparatively primitive 

 form, 1 with the small foramen which shows that the shell did not 

 live where it had to resist wave-action ; while the Cinctee are forms 

 which are also very little developed, and are particularly noticeable 

 for the smallness of their pedicle-opening — a feature more to be 

 taken account of in Terebratuloids than in Khynchonellicls — 

 because, with the former, the pedicle-opening is generally much 

 larger than that possessed by the latter. 



Bifericeras lulielhtm is an interesting little species, which 

 Mr. Ilichardson has figured in his pi. ii, figs. 29 & 30. Its 

 generic position is perhaps a somewhat rash surmise on my part, 2 

 though its likeness to the larval stage of Bifericeras (B. parvum) 3 

 is noticeable. But this point, which must be a subject for future 

 study, does not affect the interesting problem now presented by 

 the records of this little species. It has not yet been found in 

 Scotland, where Ecliioeerata are so pronounced ; it is a Yorkshire 

 form recorded from two beds of blue shale connected with later 

 forms of Echiocerates (aplanatum and macdonnellii, Kaasayan 

 0, 5) ; it has been found by Dr. W. D. Lang in situ in Dorset, in 

 a layer to itself, between two layers of crassicostate Echiocerata 

 ( Kaasayan 4). and I have specimens from the same locality, position 

 unknown , but in Gloucestershire it seems to be unaccompanied by 

 any Ecltiocerata of the required style, and appears to stand as the 

 sole representative of ])ost-si/bplaiiicosta Kaasayan fauna. These 

 points of evidence are set out in Table VI. 



Table VI. — Steatigbaphical Records of Amj/oxites tubellus. 



Yorkshire. Gloucestershire. Dorset. 



17. Ammonites tubellus. 



18. JEchioceras aplanatnm. 



19. Ammonites tubellus. 



20. Echioceras macdonnellii. 

 Ammonites tubellus. 

 Deroeeras aft', miles. 



103. Crassicostate Echiocerata. 

 100. Echioceras cf. boreale. 



Ammonites tubellus. 



Echioceras rhodanicum. 

 00. Crassicostate Echiocerata. 



1 Posteriorly it shows the primitive inveited (that is, dorsally sulcate). 

 norella stage ; it is mainly smooth, only having just begun to acquire ribs. 



2 II, 6, p. 70, footnote 1. 3 II, 4, pi. exxvii. 



