104 FOSSIL ESTHERDE. 



present relatively large, oval, Anodon-like valves (PI. IV, fig. 1), more acute behind than 

 before ; also some small, oblong, probably young valves (figs. 2 and 6) ; and thirdly, 

 a suborbicular individual (fig. 3), curiously analogous to the subquadrate or suborbicular 

 forms of E. Manga-licnsis (PI. II, figs. 20, 23) and E. striata (p. 26, fig. 2). The shape 

 of the last reminds us of some American Unios. 



Behind, the hinge-line (which in most specimens is equal to more than half the length 

 of the valve) is lost in the curved slope of the postero-dorsal region ; in front, it is ended 

 by the umbo, which projects at the antero-dorsal angle above the convexity of the anterior 

 margin, except in the young individuals from Hanover, in which case it is much less 

 distinct (PL IV, figs. 2 and 6). 



The surface of the valves bears twenty, and often many more, concentric ridges, which 

 arc usually much crowded towards the ventral border. The ornament of the interspaces 

 consists of transverse wrinkles or vertical bars, sometimes branched and inosculating. 

 These are coarser in the English variety (PL III, figs. 20 — 29) than in the German 

 specimens (PL IV, fig. 7). The concentric ridges are often so closely set that the 

 sculpturing is obsolete (figs. 4 and 5). In some specimens, from near Hastings, the 

 lower edges of the ridges are delicately crenate (PL III, figs. 28, 29). Occasionally a 

 granulate ornament accompanies the little vertical bars (fig. 20, from Bulverhithe). 



The sculptured interspaces of E. elliptica are imitated in two recent Estherice. 

 E. donaciformis, Baird ('Proc. Zool. Soc./ 1849, p. 89, Annul., pi. 11, fig. 5), from 

 Africa, has the inosculating wrinkles; and E. aw^'/es, Baird (op. cit., p. 90, pi. 11, fig. 7), 

 from India, has the short, vertical bars, together with an exaggerated crenulation or 

 beading of the concentric edges. These Estherice also more or less resemble E. elliptica 

 in the shape of the carapace. 



Of the North German specimens with which I was kindly supplied in 185S by my 

 friend, Professor Dr. W. Dunker, of Marburg (who also gave to Dr. Mantell the fine 

 specimens now in the British Museum, and figured in PL IV, figs. 1 — 7), we learn, 

 from his 'Monographic der Norddeutschen Wealdenbildung ' (4to, Brunswick, 1S46), 

 that they occur in the black Cyrena-shale, with Cypridce} of the Obemkirchn and 

 Siidhorst districts in Hanover. 2 He describes them as follows : 



"Ext/teria elliptica, p. 61 (Dunker, ' Progr.,' p. 41 ; 'Stud.,' p. 175).— Estheria valvis 

 ellipticis, planiusculis, tencrrimis, membranaceis, concentrice leviter sulcatis et striatis, 

 umbonibus obsoletis." The length is given as from 3§'" to 5'" and more; and in 

 proportion to the height as 100 : 75. 



Estheria xubquadrata (p. 62) is described as somewhat smaller, less arched on the 

 dorsal and ventral borders, and subquadrangular. This is probably immature (figs. 2 

 and 6 of our PL IV). The English variety, though adult, retains this form. 



1 See further on, Appendix. The Cypridce are calcareous; (ho shale and the Estheria are not. 

 - The Wealden area of North Germany is also described in Giebel's ' Gaea Gennaniea.' p. 2">1, &c. 



