312 MR. S. S. BUCKMAX O^^ [vol. Ixxili, 



certainly be drawn, that the special 2Iicroderoceras-Arietites fauna 

 did not occup}'^ the horizon of either turneri or hirchi, other\vise 

 they should be found in the areas where those species occur ; and a 

 second inference may more tentatively be made — that the Micro- 

 deroceras and Arietites did not occupy the same horizon. 



If it were possible to proceed on strictly biological lines, then a 

 solution would be quite easy ; but biological and geological position 

 are not always in accord : ^iplieroceras aboA'e Jlicroderoceras, 

 Faltopleuroceras later than Amaltheus, Hildoceras after J2«r- 

 poceras in geological position, when they should respectiyely preced-e 

 biologically. But these are distinct genera : in regard to species, 

 Sarpoceras exarafum below S. falciferum, Hildoceras hifrons 

 below H. semipolitum, Arietites turneri below A. brool'i^ and 

 this again much below A. denotatus, show yery well the agreement 

 of geological position and biological deyelopment. 



In the present case the assumption of the agreement of bio- 

 logical and geological position is all that there is to go upon. No 

 record of the Barrow exposure seems to haye been made. Speci- 

 mens were yery few, so I understand, for the great area opened 

 up; and what haye been saved were only the finds Avhich the 

 jiavvies took the trouble to bring home with them. 



The matrix of the Barrow Gurney exposure is a hard blue Lias, 

 which weathers or decomposes to a soft white, almost chalky 

 substance. This matrix is quite unlike any other with Avhich I 

 am acquainted in the South- West, and it w^ould serve well to 

 distinguish Barrow specimens. I find, however, that some speci- 

 mens in my father's Cheltenham collection show a similar matrix, 

 perha])s rather more cream-coloured ; and \Yright savs of his 

 Arietites turneri \_A. aff. tur(/escens~\ : 



' The specimen fignred was collected from a light- coloured clay and limestone 

 in the deep cutting of the Bristol & Birmingham Railway, near Bredon 

 ["Worcestershire], associated with A. Bonnardii, d'Orbigny, [Arietites aff. 

 plotti (Eeynes)], A. semicostatus. Y. & B., [Arnioceras hodleyi (J. Buckman)], 

 and several other mollusca, with many fragments of the stems and side 

 arms oi Pentacrinus tuherculatus. Miller, and Cidaris Edivardsii, Wright.' ^ 



The character of matrix and the remarks about the Pentacrinus 

 well fit the condition of A. hirchi J. Buckman (Jlicroderoceras 

 sejJtic/erutn) ; and, though it is labelled Cheltenham, yet Bredon 

 is quoted as a locality for A. hirchi,^ and I suspect that the 

 label ' Cheltenham ' possibly denoted in such cases ' Cheltenham 

 district,' just as 'Yale of Grioucester' was possibly used to include 

 Bredon. Judging by the light-coloured matrix it may be suggested 

 that from Bredon came my father's holotype and various paratypes 

 of Ammonites lialecis, the figured specimen and another with 

 perhaps a third of ,his A. erugatus (^Agassiceras), the specimen 

 he called^, costatus {Agassiceras\ two paratypes of his A. hodleyi, 

 and the present holotype of Jlicroderoceras septigerum. 



^ Proc. Cotteswold Nat. F. C. vol. iii (1864) p. 177. repeated in ' Monogr. 

 Lias Ammonites ' 1881, p. 293 ; see below, (e) p. 318. 

 ' Geology of Cheltenham ' new ed. 1844, p. 88. 



