113 
PLAG10ST0MA concentrica. 
TAB. DLIX.— /g. 1. 
Spec. Char. Elliptical, oblique, convex, ornamented 
with many longitudinal striae and a few regular 
concentric lines ; hinge-line short ; shell thin. 
A neatly marked slender shell, whose greatest diame- 
ter is about double the least : it is most convex towards 
the beaks, which are but a little produced. 
One of the many discoveries made by R. I. Murchison, 
Esq. in his late tour to the North of Scotland. It was 
found in a block of gray argillaceous Limestone, accom- 
panied by Ammonites, upon the beach at Ethie, near 
Cromarty. 
PLAGIOSTOMA elongata. 
TAB. DLIX.— /g. 2. 
Spec. Char. Obliquely elliptical, convex, costated; 
costae few, distinct, rounded; hinge-line short. 
Syn. Plagiostoma. Mantell , Geology of Sussex, 
p. 129. t. 19./. 1. 
The longest diameter of this Plagiostoma is equal to 
twice the shortest. The costse are about fifteen or six- 
teen, prominent, rounded and smooth : they produce 
undulated margins to the valves. 
An inhabitant of the Gray Chalk Marl and Upper 
Greensand. The upper figure is from a specimen found 
at Folkstone; the other from one presented in 1814 by 
Mr. Mantell, who obtained it at Hamsey. 
