. Bulletin of the British Museum (Natural History), Geology. OF NORTH-WEST EUROPE 321 C. posticalis parisiensis are exactly the same, but the great variation within the sample is taken to indicate subspecific differentiation. C. klahni Stchepinsky from the Stampian Marnes a Cyrenes of Alsace has orna- mentation confined to the median and posterior parts of the valve and consists of double rows of small puncta. In this respect it is similar to some of the specimens of C. posticalis parisiensis. However, the lateral outline has a rhomboidal appearance due to the shape of the posterior margin, wh
. Bulletin of the British Museum (Natural History), Geology. OF NORTH-WEST EUROPE 321 C. posticalis parisiensis are exactly the same, but the great variation within the sample is taken to indicate subspecific differentiation. C. klahni Stchepinsky from the Stampian Marnes a Cyrenes of Alsace has orna- mentation confined to the median and posterior parts of the valve and consists of double rows of small puncta. In this respect it is similar to some of the specimens of C. posticalis parisiensis. However, the lateral outline has a rhomboidal appearance due to the shape of the posterior margin, which differs from C. posticaUs; and in dorsal outline it is more tapered. It is much smaller, but is probably a related species. Dimensions : Left valve Right valve L H L/H L H L/H Female 0-95 0-53 179 0'9i 0-47 1-94 Male 1-05 0-53 1-98 1-03 0-49 2-10 Cytheretta headonensis Haskins (PL 18, figs 11-14; Text-fig. 24) 1857 Cytherideis colwellensis Jones (pars) p. 49, pi. 14, figs 2oa-c. 1870 Cythere ? Jones p. 157 and 159. 1887 Xestoleberis aurantia non Baird, var. Jones and Sherborn, vol. 4, p. 456. 1889 Cytherideis colwellensis Jones, Jones and Sherborn p. 45. 1968 Cytheretta rhenana headonensis, Haskins, p. 167, pi. 3, figs 11-18. Diagnosis: An unornamented species of Cytheretta with a strongly obliquely rounded anterior margin. Material: 3 valves from Headon Hill; 16 from Colwell Bay; 17 from Milford; 7 from Whitecliff Bay. lo 4043-7. Type locality and horizon: Although there are grounds for believing that Headon Hill is the type locality due to etymology, in the type description Whitecliff Bay is quoted; Middle Headon Fig. 24. Cytheretta headonensis Haskins; female right valve; X75. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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