34 CRETACEOUS LAMELLIBRANCHIA. 



Affinities. — See A. Sanctse-Crucis (below). The external teeth are more oblique 

 in this than in most forms of Area, in which respect it may be compared with 

 A. equidens, Tate. 1 



Distribution.— Lower Greensand of Upware. Atherfield Beds of East Shalford 

 and Peasmarsh. ? Perna-bed of Redcliff. 



Aeca Sanct.e-Ckucis, Pictet and Campiche, 1866. Plate VI, figs. 6 a — c, 7 a — c. 



1S66. Aeca Sanct^-Crucis, F. J. Pictet and G. Campiche. Foss. du Terr. Cret. 

 de Ste. Croix (Mater. Pal. Suisse, ser. 4), pt. 3, 

 p. 437, pi. exxx, figs. 10, 11. 



Description. — Shell elongate, very convex in the umbonal region ; wedge-like 

 posteriorly. Anterior margin rounded, more or less perpendicular to the hinge- 

 line. Ventral margin a little sinuous, more or less parallel to the dorsal. Poste- 

 rior margin nearly straight, and either at right angles or slightly oblique to the 

 hinge-line. Umbones prominent, incurved, placed near the anterior third of the 

 shell. Carina rounded ; postero-dorsal area depressed, sometimes slightly con- 

 cave, with one or two faint broad ridges. Hinge-area long and broad. Orna- 

 mentation consists of numerous fine radial ribs crossed by lines of growth. 

 Interior not seen. 



Measurements : 



(i) (2) 



Length . . . .31 . .25 mm. 



Height . . . .17 . . 14 „ 



Thickness . . . 16*5 . . 13 „ 



(1) and (2) are from Upware. 



Affinities. — This form agrees in many respects with A. Carteroni, d'Orbigny, 

 and it is likely that a large series of specimens would show a passage between the 

 two. At present I have seen only three or four examples of each. Area 

 Sanctse-Crucis appears to differ from A. Carteroni in being proportionately 

 shorter, in having the ventral margin sinuous and less parallel to the dorsal, and 

 in the umbones being more prominent and incurved. 



It also appears to be similar to Area autissiodorensis, Cotteau, 2 but seems to be 

 less inflated and to have the posterior margin less oblique. 



1 'Trans. Koy. Soc. S. Australia,' vol. viii (1886), p. 139, pi. xi, fig. 9 ; G. F. Harris, ' Cat. Tert. 

 Mollusca' (Brit. Mus.), part i (1897), p. 331. 



2 'Moll. Foss. de l'Yonne' (1855), p. 86; de Loriol and Cotteau, ' Mon. Pal. Geol. de Port- 

 landien de l'Yonne ' (18G8), p. 179, pi. x, figs. 6, 7. 



