2 EOCENE MOLLUSCA. 
cordatis ; lunuld excavatd, ovato-oblonga ; latere antico brevi, late obtuso, postico oblique 
truncato ; cardine crasso, unidentato, altero inaqualiter bidentato ; dentibus crassis trian- 
gularibus ; irregulariter sulcatis ; cicatriculd musculari anticd profundd.’ (Deshayes.) 
“Var. B. Testa suborbiculari, inflato-cordatda. 
Var. y. Testa brevi, subquadratd, postice transversim vel paulo obliqué truncata. 
Var. 8. Testdé ovato-oblongd, postice truncata. 
Var. <«. Testa ovatd, paulo arcuatd postice magis elongato-attenuatd. 
Length 2% inches ; height 14 inches. 
Localities. Britain: Dulwich. (J/eyer.) 
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 (Kocene 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 Unio 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 ‘ Hocene Bivalves,’ p. 131). Our present shell is not very far removed from 
the recent species Unio complanatus. 
Dreissena serrata, Melleville (‘ Sables Tert. inférieurs, p. 40, pl. 1, f. 11, 12), is 
inserted in the List given by Mr. Whitaker in his memoir, p. 577, as from the Woolwich 
and Reading 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. 
CYRENA. 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 
