428 CRETACEOUS LAMELLIBRANCHIA. 



licmiirks. — The type cannot bo found, but other specimens named by Forbes 

 are in the Museum of Practical Geology (Geological Society Collection, Ko. 2217). 

 DistiibiUioii. — Lower Greeusand (Crackers) of Atherfield. 



Unicahihum ? coMi'KKSSUM, fip. HOC. Plate LXII, figs. 5, G. 



[Omitted from Vol. II, p. 163.] 



Description. — Shell convex, with flattened or slightly concave flanks, oval or 

 subipiadrate, moderately or slightly inequilateral. Anterior margin rounded; 

 posterior margin subtruncate, slightly oblique, curved ; ^•entral margin nearly 

 straight and nearl}^ parallel to the dorsal margin. Umbones broad, close 

 together. A rounded carina extends from the umbo to the postero-veutral 

 extremity, limiting the compressed postero-dorsal region. External ligament l)road. 

 Ornamentation consists of a few coarse somewhat irregular concentric ribs, which 

 are sometimes rugose, with finer ribs in the interspaces. 



Measurements : 



(1) (2) 



Length 40 . 32 mm. 



Height 2(3 . 22 „ 



Thickness . . . . . . .17 . — „ 



(1, 2j Crackers, Atherdeld. 



Affinities. — The hinge and interior of this species have not been seen, conse- 

 qnently its generic position cannot at present be definitely determined, but it is 

 provisionally referred to Unicanlium on account of its external resemblance to 

 some Jurassic species of that genus. U.? cowpressum is similar to some forms of 

 Jl/yrt vngosa, Romer,^ which has been referred to the genus Lucina by de Loriol 

 and Cotteau, to Mactwintjn by Agassiz, and to Unicanlium by Zittel. 



Ti/pe. — From Atherfield, in the Sedgwick Museum, Cambridge. 



Distribution.— Lowev Greensand (Crackers), of Atherfield. Atherfield Clay of 

 Dover Colliery. 



Unicakdium r Maillhanltm {tVOrhiijuij), 181k Plate LXTL figs. 7—9. 



[Omitted from Vol. II, p. 1651. 



1844. Cakdium Mailleanum, A. d'Orhiijuij. Pal. Fran^'. Terr. Cret., vol. iii, p. 



40, pi. celvi, figs. 7—12. 



' See especially de Loriol ami Cotteau, ' Mou. I'ak'out. Gcol. I'ortlaudieu de I'Y'ouue" (1868), 

 p. 135, pi. ix, figs. 10, 11. 



