82 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 
Oxfordian Oolites ; for although it occurs in the Cornbrash of Yorkshire and Wiltshire, it 
is rarely found in a lower position than the Kelloway Rock. Roemer records his Lutraria 
sinuosa in the Lower Coral Rag of Heersthum; Agassiz places his Plewromya recurva in 
the Terrain 4 Chailles of Chamsol, in the department of Doubs. 
Myacites sInistRA, Agassiz,sp. Tab. XXXV, figs. 17,17 a. 
Arcomya sINIsTRA, Agassiz. Et. Crit. Myes., p. 170, tab. 9, figs. 1—3, et tab. 9’, 
figs. 10—13. 
Panop#a sINistTRA, D’Orb. Prodr., i, p. 273. 
—_ -— Oppel. Juraformation, p. 480. 
Testa ovato-elongata antice attenuata, postice conveaa producta, margine hante, 
umbonibus subcompressis, depressis, antemedianis, latere antico oblique-declivi, lunula 
concavo, margine superiort subhorizontali margine inferiore subrecto; valvis lateribus 
plicis irregularibus crebis longitudinalibus, et sulco superficial antemediano oblique-dechwit. 
Nucleus glaber. 
Shell ovately elongated, with the sides of the valves rather flattened; anterior side 
attenuated, its margin sloping obliquely downwards ; lunule concave ; posterior side more 
convex and lengthened, its superior border nearly horizontal ; the posterior extremity is 
somewhat rounded, with an aperture moderately large ; the umbones are depressed, and 
somewhat compressed laterally ; they are placed a little posterior to the anterior third of 
the shell, and there is a slight sulcation, which proceeds from them obliquely forwards and 
downwards towards the lower border; the inferior margin is lengthened and nearly 
straight; the surface of the test has numerous irregular and rather delicate longitudinal 
plications ; the granules over the greater portion of the valves are so minute and crowded 
that they cannot be traced to form connecting lines, but towards the sides they are larger, 
more distantly arranged, and distinctly linear; the test upon the anterior side is of 
moderate thickness, posteriorly it is much thinner; the nucleus is smooth, and exhibits 
the adductor and pallial scars. 
Length, 2 inches; height, 1 inch; diameter through both the valves, # inch; but our 
specimen is imperfect, and appears to have lost about 2 lines in length at the posterior 
extremity. 
The more depressed umbones, the anterior attenuation, and the nearly horizontal 
figure of the superior border, will serve to distinguish it from all the varieties of Pleuromya 
elongata, Ag., to which it bears some resemblance. 
The Arcomya sinistra of Quenstedt, ‘Der Jura,’ p. 451, tab. Ixii, fig. 2, from the higher 
stage of the Inferior Oolite, occurs also in the same position in the vicinity of Cheltenham ; 
it is, however, distinct from A/yacites sinistra. Some varieties of Myacites decurtatum 
approach to it in the general figure, but are readily distinguishable when the granulated 
