ZONE OF ARIETITES RARICOSTATUS. 



55 



Lamellibranchiata. 



Gryphsea obliquata, Lamk. 

 Ostrea Goldfussi, Bronn. 

 Pecten priscus, Schloth. 



— aequalis, Quenst. 



— calvus, Gold/. 

 Lima gigantea, Sow. 



— pectinoides, Sow. 

 Monotis inaequivalvis, Sow. 

 Pinna folium, Young ^ Bird. 



— Hartmanni, Ziet. 

 Leda Heberti, Mart. 



— subovalis, Qoldf. 



— Galathea, d'Orb. 



Cidaris spines. 

 Acrosalenia minuta, Buck. 



Cucallsea Miinsteri, Ziet. 

 Modiola scalprum, Sow. 

 Protocardia oxynoti, Quenst. 

 Astarte obsoleta, Bunk. 

 Nucula navis, Piette. 

 Hippopodium ponderosum, Sow. 

 Cardinia hybrida, Sow. 

 Unicardium cardioide, PJiill. 

 Homomya ventricosa, Agass. 

 Arcomya vetusta, Phill. 

 Gresslya Galathea, Agass. 

 Rhynchonella calcicosta, Quenst. 

 Ehynchonella oxynoti, Quenst. 



BCHINODERMATA. 



Pentacrinua tuberculatus, Mill. 

 — basaltiformis, Mill. 



1. The Zone of Arietites raricostatds. 



Synonyms. — " Hippopodium-bed " (pars), Murchison's ' Geology of Cheltenham,* 

 2iid ed., by Buckman and Strickland, p. 44, 1845. " Raricostatenschicht," Fraas, 

 ' Wiirttemb. naturw. Jahreshefte,' pi. 3, 1847. "Die Schichten des Jimmnifes rari- 

 cos^ate," Oppel, ' Die Juraformation,' p. 56,1856. " Raricostatenbank," Quenstedt, 

 ' Der Jura,' p. 293, 1858. " Raricostatus-bed," Wright, ' Quart. Journ. Geol. Soc.,' 

 vol. xiv, p. 25, 1858. "Zone of Ammonites raricostatus," Wright, 'Quart. Journ. 

 Geol. Soc.,' vol. xvi, p. 407, 1860. "Die Schichten des Ammonites zipJms" (pars), 

 Brauns, 'Die Untere Jura,' p. 90, 1871. 



The beds forming this zone are exposed in several brick-fields in the Vale of 

 Gloucester. They consist of dark-coloured clays, more or less impregnated with 

 ferric oxide. In an excavation made at Marie Hill, near Cheltenham, for brick- 

 earth, the following section was obtained. The beds are enumerated in descending 

 order. 



No. ft. in. 



1. Gryphcea-bed ; a hard, ferruginous clay, which broke into fragments, and contained 



a great many specimens of 6r;)/^^tEa oi/zywa^a. Sow 3 ft. to 4 



2. Coral-band ; a thin seam of lightish-coloured unctuous clay, containing a great 



many small, sessile Corals, Montlivaltia rugosa, Wrt., most of which appeared to 



have been attached to the curved valves of the Gry/jAffla 1 in. to 1^ 



3. Hippopodium-bed ; a stiff dark-coloured clay, in some parts ferruginous ; con- 



taining Cardinia Listeri, Sow., and Hippopodium ponderosum. Sow., in consider- 

 able numbers from 8 ft. to 10 



4. Ammonite-bed ; a dark, ferruginous clay, containing selenite, ferric oxide,""] 



and ferrous sulphide, and great numbers of a highly pyritic brood of I Not 

 Aegoceras subplanicosta, 0pp., Aegoceras densinodum, Arietites raricostatus, [ascertained. 

 Arietites Nodotianus, and the other species of the list J 



