ALBIAN FOSSILS DISCOVERED AT OKEFORD FITZPAINE. 7l 



KANGE OF SPECIES. Basal zone of the Albian formation. 

 LOCALITIES. Maidstone, Crockerton, Warminster, Devizes, 

 Folkestone, Dorking, &c., and from France, Switzerland, &c. 



MOLLUSCA, Lamellibranchiata. 

 PLEUROMYA PLICATA, J. de C. Sowerby. 



PI. ii., figs. 4-5. 



Mya plicata, J. de C. Sowerby : Mineral Conchology, 1823, 

 Vol. 5, pi. 419, fig. 3, p. 20. 



Panopcea plicata, J. de C. Sowerby: Mineral Conchology, 1840, 

 Vol. 7. Alphabetical Index, p. 6. Orbigny : Paleontologie 

 Franchise, Terrains Cretaces, Larnellibranchia, 1843. PI. 357, 

 fig. 4-5, p. 337. 



Mijopsis plicata, Agassiz : Etudes Critiques Mollusques Fossiles, 

 1840, p. 253. 



This species, of which there are two examples, refers to an 

 oblong and ventricose shell with valves gaping at both extremities, 

 though mostly so posteriorly ; the beaks are anterior and incurved, 

 beneath them being a deep concavity ; shell structure thin and 

 ornamented in places with obscure, minute, granular striations ; 

 the larger ornamentation consists of regular, thick concentric plicae 

 obtusely angulated posteriorly, where they incline upwards to the 

 dorsal line and form a more or less truncated end. 



Some discussion has arisen as to the merits of Agassiz's two 

 genera, Pleuromya and Mijopsis, both of which present the same 

 general features. Terquem* made a special study of them in 

 1853, and came to the conclusion that Pleuromya should be adopted 

 and that Mijopsis should be included in its synonomy, a plan 

 which has been followed by most paleontologists, and which is 

 recognised on the present occasion. 



Dimensions Height = 44 \ 



Length = 70 I Millimetres. 

 Depth, both valves attached = 40 J 



* Bull. Soc. Geol France, 1853, Ser. 2, Vol. 10, Pi. 10, p. 534. 



