148 THE LIAS AMMONITES. 



M. Marcou,^ in his ' Jura Salinois/ has described some beds as "Marnes a Trochus 

 oil de Pinperdu," which contain the leading fossils of the " Jurensis-MergeV In other 

 Departments of Erance the same species of Ammonites have been collected, as, for 

 example, near Fontenay (Vendee) ; Charolles, Saone-et-Loire ; Mont d'Or, near Lyons,. 

 Rhone ; Semur, Cote d'Or; &c., so that the Jurense-ione forms a well-defined horizon of 

 life in the uppermost portion of the Upper Lias of Erance. 



16. Zone of Harpoceras opalinum, 



" Opalinus-Thone," Quenstedt, 'Elozgeb. Wiirtemb.,' pp. 281, 539, 1843. 

 "Schict. des Am. toruhsus," pars, Oppel, ' Jura-Eormation,' p. 306, 1855. "Zone a 

 Avi. opalinus," Reynes, ' Geol. etPal. Aveyron,' p. 63, 1868. "Zone a Am. opalinus" 

 pars, Dumortier, ' Bassin du Rhone,' tom. iv, p. 278, 1 874. " Thone der Trigonia 

 navis,'^ pars j "Zone des "Am. tondosus'" Lepsius, 'Jura-Formation Unter-Elsass,' 

 pp. 3, 14, 1875. 



This zone was formerly grouped with the Cephalopoda-bed at Erocester ; but, as it 

 contains some species which are limited to this horizon and are associates of Harpoceras 

 opalinum, it is best to treat it as the highest zone of the Lias. At Haresfield it forms a 

 thin band of hard, ferruginous marl, which lies at the base of the Inferior Oolite in 

 conformable position thereto. From this I have collected Harpoceras opalinum. Rein., 

 Macrodon Hirsonensis, d'Arch., Terehratula punctata, David., var. MhgncJionella cyno- 

 cepliala. Rich., Bliyn.furcillata, Theod. I have had few Ammonites from this bed, and 

 the other shells are not abundant. At Erocester Hill the upper portion of the Cephalo- 

 poda-bed contains several Ammonites, which have been described and figured by my old 

 and esteemed friend Dr. Lycett." One of these, Harp. Moorei, appears to resemble so much 

 several specimens of Harp, opalinum from Gmiind, Boll, and Gundershofen, that I have 

 no hesitation in regarding Harp. Moorei as a variety of Harp, opalinum, the form of 

 the keel and the fine lines on the shell clearly showing the affinities. These localities are 

 the only two I know in Gloucestershire, where this Ammonite is found. In Dorsetshire 

 I have collected large beautiful specimens at Burton Bradstock, and at Chideock Hill, 

 near Bridport, and have always found this species immediately beneath the Inferior 

 Oolite. From the Haresfield bed I have taken a piece of rock having the impression of 

 Harp, opalinum on its underside, whilst the block itself contained Inferior OoHte 

 fossils ; a fact which may afford an explanation how this Ammonite is considered by 

 some to be an Oolitic species, and the progenitor of Harp. MurcMsonce. The Opalinum- 



1 ' Jura Salinois,' pp. 54 and 66, 1846. 



2 'The Cotteswold Hills Handbook,' p. 122, pi. i, fig. 2, 1857. 



