102 CRETACEOUS LAMELLIBRANCHIA. 
Remarks.—Two incomplete specimens in Mr. Me¥er’s collection agree with M. 
(Brachydontes) Guerangeri, from the Cenomanian of Le Mans, except in having finer 
ribs. Not having seen the type or other French specimens of M. Guerangeri 1 am 
unable to refer these examples definitely to that species. The ribbing on the 
ventral surface is clearly shown, and separates this form from M. divaricata, 
VOrbigny.' 
A specimen from the Greensand of Haldon, in Mr. Vicary’s collection (pl. xvii, 
fig. 4), agrees with M. Guerangeri, especially with the example figured by 
Guéranger, except in the absence of the fine ribbing on the ventral surface; this 
difference may be due to imperfect preservation. The shell tapers more rapidly 
toward the umbones than in M, divaricata. 
Distribution.—Greensand of Haldon. Cenomanian (Me¥er’s Beds 10 and 12) 
of Dunscombe. 
Moprona (BRACHYDONTES) VECTIENSIS, sp. nov. Plate XVII, figs. 6 a, b, 7 a—e, 8. 
Deseviption.—Shell small, rather short, inflated, expanded, and compressed 
posteriorly, extremities rounded. Ventral margin with a sinus produced by a 
mesial depression. Umbones obtuse, not terminal. Ornamentation consists of 
many strong and somewhat irregular ribs, which cover the entire surface and 
generally bifurcate toward the margin of the valve. 
Measurements : 
(1) (2) (3) (4) (4) 
Length . : : ; . 14 147 3:5 1225) 9mm. 
Height . : : : on 8, 8S oe 
Thickness ; : ude XG —- —- — —, 
(1), (5) from the Crackers, Atherfield. 
(2) from the Perna-bed, Redcliff. 
(3) from the Atherfield Beds, Littleton Pit, near Guildford, 
(4) from the Atherfield Beds, East Shalford. 
Affinities.—The smaller forms of this species resemble M. striato-costata 
(VOrbigny), but possess stronger and less regular ribs, and are without the con- 
centric ribs. 
M. morinicus’ (de Loriol) is also similar, but has more regular ribs, which do not 
bifureate, and some parts of the shell are without ribs. 
1 «Pal. Frang. Terr. Crét.,’ vol. iii (1844), p. 275, pl. ecexl, figs. 3, 4; ‘Prodr. de Pal.,’ vol. ii 
(1850), p. 246; Pictet and Campiche, ‘ Foss. Terr. Crét. Ste. Croix’ (1867), p. 511. 
* De Loriol and Pellat, ‘ Portlandien de Boulogne-sur-Mer’ (‘ Mem. Soe. Phys. et d’Hist. Nat. de 
Genéve,’ vol, xix, 1866), p. 91, pl. ix, fig. 4, 
