1 1 i 
PLAGIOSTOMA Hoperi. 
TAB. CCCLXXX. 
Spec. Char. Transversely ovate, oblique; 
valves convex, obscurely punctato-striated ; 
striae diverging, deepest upon the sides ; an- 
■ terior slope straight, concave. 
Syn* Plagiostoma Hoperi, Mantell GeoL of 
Sussex, 204, tab. 26, f. 2, 3 ,f. 15. 
Nearly smooth between the longitudinal striae, which 
are very commonly so obscure as not to be traced, except 
close upon the sides, or near the edge : they are marked 
with punctums in the same manner as P. punctata ; the 
ears are unequal, not very prominent, they are striated. 
Sent me long ago by G. A. Mantell Esq. from Lewes ; 
it occurs also at Northfleet, and other parts of the Chalk 
range not rarely. 
I fear that a single valve of this very distinct shell, 
although similar in form, has been confounded with 
Dianchora lata, tab. 80. and given rise to its being 
described as plain, instead of striated, which the figure 
shews it to be ; the stri® indeed are deep, but close and 
regular, so that the surface has a smooth aspect. 
PLAGIOSTOMA rusticum. 
TAB. CCCLXXX1. 
Spec. Char. Transversely oblong, oblique, 
longitudinally sulcated ; valves convex ; 
sulci deep ; ears obscure ; anterior slope 
straight, convex along the middle. 
A bout 25 deep irregularly disposed, and often curved 
furrows, give the surface of this shell an unfinished 
clumsy appearance ; the spaces between the furrows are 
more or less flattened or convex, and are smooth ; they 
are irregular in width, some specimens having them 
widest in the middle, others at the sides of the valves ; 
the ears, especially those upon the anterior slope, are 
very short, and confounded with the edge of the shell ; 
the beaks are slightly prominent, the length is about two 
thirds the width. 
Fouud in clay mixed with sand, consisting of large 
green grains, upon Shotover Hill, near Oxford. 
