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EOCENE MOLLUSCA. 



cordatis ; lunula excavatd, ovato-oblongd ; latere antico brevi, late obtuso, postico oblique 

 truncato ; car dine crasso, unidentalo, alter o incequaliter bidentato ; dentibus crassis trian- 

 gularibus ; irregulariter sulcatis ; cicatriculd musculari anticd profunda." {Deshayes.) 

 " Far, (3. Testa suborbiculari, inflato-cordatd. 



Far. y. Testa brevi, subquadratd, postice transversim vel paulo oblique truncatd. 

 Var. <>. Testa ovato-oblongd, postice truncatd. 



Var. e. Testa ovatd, paulo arcuatd postice magis elongato-attenuatd. 



Length 2^ inches ; height \\ inches. 



Localities. Britain : Dulwich. {Meyer.) 



France: Cuis. (Deshayes.) 



The specimen of this genus from the Lower Eocene of Dulwich, of which the figure 

 above referred to is a representation, was obligingly sent to me for examination by Mr. C. 

 J. Meyer, with the name of U. Solandri ? written upon it ; but I think that it can hardly 

 be referred to that species. The specimen is a cast of the interior with a very small 

 portion of the shell remaining, and the form is so different from that of Solandri, and 

 approaches so closely to the second variety described by M. Deshayes of the very variable 

 species Michaudi, that I have so referred it provisionally. The shell figured by myself 

 under the name of U. subparallelus (Eocene Moll., T. XX, f. 13) appears to be pro- 

 portionally so much longer that I think our present specimen must belong to a different 

 species. The true determination of some of the recorded Lower Eocene shells of this 

 genus will require better specimens than any I have seen, but I doubt much if any that 

 I have seen can be correctly referred to Vnio Solandri, although in this genus especially 

 we are confronted with more than ordinary variation, when we consider the enormous 

 amount of synonyms that have been given by Mr. Lee to some of the living British 

 species (see 'Eocene Bivalves,' p. 131). Our present shell is not very far removed from 

 the recent species Vnio complanatus. 



Dreissena serrata, Melleville ( £ Sables Tert. inferieurs, p. 40, pi. 1, f. 11, 12), is 

 inserted in the List given by Mr. Whitaker in his memoir, p. 577, as from the Woolwich 

 and Beading series, but for this no special locality is given, and I have not been able 

 to see a specimen to justify the name. This was inserted by him, he informs me, on the 

 authority of Mr. Prestwich's list in 'Quart. Jour, of the Geol. Soc, vol. x, p. 117, 

 wherein Mr. Prestwich says that the specimen on which the name is inserted by him 

 was too imperfect to admit of a positive determination. 



CYBENA. Lamarck. 



Generic Character. Shell equivalved, roundedly trigonal, ovate, or transverse, more 

 or less inequilateral, generally thick and strong : hinge with two cardinal teeth in each 

 valve and a large extended lateral tooth on both sides ; exterior generally smooth or 



