. Bulletin of the British Museum (Natural History), Geology. 36 BRITISH LOWER JURASSIC _h_ o/ C rugulo. â O. 40 60 length mm Fig. g. A stratigraphical sequence of British rugoid cardiniids ; oldest at the top, youngest at bottom. The diagram represent height : length ratios in Cardinia rugulosa, Jamesoni Zone ; C. dayi, Margaritatus Zone ; C. tutcheri, Spinatum Zone ; and the French specimen, () 66216, from the Whitbian Substage at Fontaine Etoupefour. The tendency towards elongation in the development of C. rugulosa, and also in the sequence of C. dayi, C. tutcheri and specimen 66216,
. Bulletin of the British Museum (Natural History), Geology. 36 BRITISH LOWER JURASSIC _h_ o/ C rugulo. â O. 40 60 length mm Fig. g. A stratigraphical sequence of British rugoid cardiniids ; oldest at the top, youngest at bottom. The diagram represent height : length ratios in Cardinia rugulosa, Jamesoni Zone ; C. dayi, Margaritatus Zone ; C. tutcheri, Spinatum Zone ; and the French specimen, () 66216, from the Whitbian Substage at Fontaine Etoupefour. The tendency towards elongation in the development of C. rugulosa, and also in the sequence of C. dayi, C. tutcheri and specimen 66216, is well demonstrated by this diagram. The possibility that this might in fact be an evolutionary sequence cannot be overlooked. Measurements were made on single valves of each of the species at various growtli stages and outlines drawn as left valves for uniformity. Kilve in north Somerset C. ovalis is found in Hettangian shales and is there accom- panied by Astarte obsoleta Dunker, in the proportion of 10-15 Cardinia to 1 Astarte. The only other associates, apart from ammonites, are rare oysters and even rarer scaphopods. The same two species are also found in Hettangian shales at Evesham, Worcestershire, where the ratio is about 15-20 Cardinia to 1 Astarte, but there the association is masked by the presence of other bivalve molluscs, particularly Liostrea irregularis (Minister). At a higher horizon in the Frodingham Ironstone of Lincoln- shire, Cardinia and Astarte also occur together, but there the Astarte is rare, and the estimated ratio is about 50-100 Cardinia to 1 Astarte. The richly fossiliferous shell beds seen at Blockley, Worcestershire, and around Cheltenham and Gloucester, Gloucestershire, are in the Ibex Zone. In Gloucester- shire both Astarte and C. attenuata are abundant in the Valdani Subzone, but in the slightly later (Luridum Subzone) shell bed at Blockley Station Astarte platymorpha Cossman (Palmer 1973 : 260) dominates to the exclusion of C. attenuata wh
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