. Bulletin of the British Museum (Natural History), Geology. AMI BRITISH LOWER JURASSIC PI. Fig. 4. Comparative hinges of right valves of : (a) Cavdinia listeri, Sinemurian of Evesham, Worcestershire. (b) C. ovalis, Hettangian of Chadbury, Worcestershire. (c) C. concinna, Whitbian, Transition Bed, Astrop, Northamptonshire. The constancy of the dentition is well demonstrated, in spite of difference of stratigraphi- cal age in 4b and 4c, and difference of shape in 4a and 4c. Notation as for Fig. 2. x \. the edge of the shell, is visible above PI, hence the Till' of Douville does not exist. Unfor
. Bulletin of the British Museum (Natural History), Geology. AMI BRITISH LOWER JURASSIC PI. Fig. 4. Comparative hinges of right valves of : (a) Cavdinia listeri, Sinemurian of Evesham, Worcestershire. (b) C. ovalis, Hettangian of Chadbury, Worcestershire. (c) C. concinna, Whitbian, Transition Bed, Astrop, Northamptonshire. The constancy of the dentition is well demonstrated, in spite of difference of stratigraphi- cal age in 4b and 4c, and difference of shape in 4a and 4c. Notation as for Fig. 2. x \. the edge of the shell, is visible above PI, hence the Till' of Douville does not exist. Unfortunately Douville failed to reveal the fact that in Cardinia the lateral teeth and sockets alternate, the anterior right tooth fitting into the anterior left socket, and the posterior left tooth into a posterior right socket. This arrangement forms a very powerful shear-resistant articulation for the two valves, and its permanence throughout the stratigraphical range of the genus argues for powerful selective forces maintaining this unique form of hinge. IV. BRITISH LIASSIC SPECIES OF CARDINIA Family CARDINIIDAE Zittel 1881 Genus CARDINIA Agassiz 1841 (= Thalassides Berger 1833, suppressed ; Ginovga Gray 1840, nom. nud. ; Sinemuria de Christol 1841, suppressed ; Pachyodon Stutchbury 1842 ; Dihora anon. 1842 ; Storthodon Zittel 1881 ; Nidarica Cox 1961.) Type species. Unto listeri J. Sowerby 1817, designated Opinion 292. The generic name was validated in the same opinion (see Cox 1951). Diagnosis. Integripalliate heterodont bivalve molluscs with unique hinge consisting of anterior laterals All and AIII, posterior laterals PI and PI I, and an obsolescent cardinal 3b. Remarks. The genus Nidarica, proposed by Cox (1961), type species C. slatteri Wilson & Crick 1889, is here considered to be a synonym of Cardinia Agassiz 1841. The external shell features distinguishing it from other cardiniids, concave lateral surfaces and very incurved beaks, are only
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