496 BRITISH PALAZOZOIC FOSSILS. [LAMELLIBRANCHIATA. 
arched from the beak to the respiratory angle; posterior slope slightly convex, so that the diagonal ridge sepa- 
rating it from the body of the shell is very broadly rounded; valves gently and evenly convex, most so near the 
middle; muscular impressions, pallial scar, and hinge-teeth, as in the generic character. Surface nearly smooth, 
with obsolete, obtuse, concentric plicze (four in two lines at middle of shell), Length one inch two lines, pro- 
portional width from beak to opposite ventral margin =, length of anterior end =, from beak to respiratory 
angle ==, depth of both valves ;z. 
Colonel Portlock’s figure above quoted represents the beak too nearly central, and the compression of the 
anterior side slightly too abrupt. The species differs entirely from the MZ. carbonaria, by the slight and uniform 
convexity of the valves, the broadly-arched diagonal ridge, and less compression of the posterior slope, smaller 
beaks, &c. 
Position and Locality Common in the lower carboniferous limestone of Lowick, Northumberland. 
MyopHoria oOBLIQUA (MW ‘Coy). 
Ref. and Syn. = Axinus obliquus M*Coy, Synop. Carb. Foss. Irel. t. 8. f. 29. 
Dese.—Obliquely ovate; beaks prominent, close to the anterior end; anterior side short, forming from 
beak to opposite point of ventral edge a nearly semicircular curve, slightly flattened towards the beaks ; posterior 
end elliptically pointed, very obliquely truncated; the posterior margin only slightly convex from the beak to the 
respiratory angle; posterior slope flattened, very steep, strongly separated by an angular ridge from the body of 
the shell, which is moderately and evenly convex, most so near the middle; ventral margin gently convex; 
muscular impressions strong; entire pallial scar strongly marked on casts. Length eleven and half lines, pro- 
portional width from beak to ventral margin {%, length of anterior end about =, from beak to respiratory 
50 
angle ;%, depth of both valves ;j;. 
This species has the shell rather thick, and the internal impressions well marked; the hinge-teeth and mus- 
cular impressions are seen to be as in the generic character, and the unsinuate pallial scar is remarkably distinct 
in most specimens. I have not seen the surface of the English examples ; but in my Volume above quoted I 
note the surface as smooth, with concentric, fine, thread-like strize on the anterior side, and that the periostraca 
in shale specimens often extends for a line or more beyond the margins. Col. Portlock’s figure (Geol. Rep. 
t. 36. f. 6.) of his Amphidesma axiniformis (which is not however the Jsocardia axiniformis of Phillips) re- 
sembles this species very closely, but has rather straighter anterior side, and less oblique truncation of the 
posterior end, and the diagonal ridge is not so strongly marked. 
Position and Locality—Common in the lower carboniferous limestone of Lowick, Northumberland. 
MYOPHORIA OBSCURA (Soi. Sp.) 
Ref. and Syn. = Axinus obscurus Sow. Min. Con. t. 314. (2 + A. parvus + A. undatus Brown, Manch. Trans. 
Vol. I. t. 6. f.30, 31. according to King) = Schizodus obscurus (Sow. sp.) King, Perm. Foss, t. 15. f. 23, 24. 
Desc.—Obovate, anterior side broad, from beak to opposite point of ventral margin, almost semicircularly 
arched; beaks large, prominent, tumid, with a slight oblique inclination towards the posterior side ; posterior 
end narrowed by the convergence of the dorsal and ventral margins, and subtruncate rather obliquely (the narrow- 
ness and obliquity increasing with age); hinge-line oblique; ventral margin moderately convex, or with a slight 
concavity in front of the respiratory angle in old specimens; valves moderately convex, most so at one-third the 
width from the beak, from whence the surface declines gradually to the anterior and ventral margins; diagonal 
ridge from the beak to the respiratory angle obtuse, moderate ; posterior slope flattened. Shell moderately 
thick, marked with obtuse, concentric, irregular strize, most regular and distinct on the anterior third, Casts 
shew the teeth, and muscular and entire pallial impressions, as in the generic character. Length of very large 
specimen one inch eight lines, greatest proportional width from beak to opposite ventral margin =, length of 
anterior end ;;;, length of hinge-line 3, width of posterior end =, depth of each valve = to 7. 
