229 
EX Alovhracia concentrica, n.sp. Pl. xxviii., figs, 12, 13, 14. FI22. 
Shell, rhomboid-oval; anterior-dorsal border straight, 
scarcely convex ; posterior-dorsal border rather more concave ; 
ventral-border uniformly slightly convex, joining the anterior 
border with a sharp curve; posterior end nearly vertically 
truncate, scarcely rounded at the superior angle, more at 
the inferior. A rounded umbonal ridge curves to the pos- 
terior inferior angle. Numerous valid, round, rude, incom- 
plete, ill-curved concentric ribs frequently overlap in the 
median area. Fine crowded, crooked, radial incisions cross 
the ribs and spaces, and interrupt more crowded concentric 
incisions, so as to produce a microscopic shagreen pattern. 
There is a depressed lanceolate dorsal area behind the umbo, 
at the margin of which the ribs cease, and which is finely 
antero-posteriorly striate. In the right valve is a very nar- 
row furrow within the dorsal borders for the edge of the 
left, valve, and its inner margin behind the umbo projects as 
a laminar tooth, soon vanishing posteriorly. The inner sur- 
face is “glistening, and has faint radial substriations. The 
pallial sinus is of moderate depth and round. 
Dimensions.—U mbo-ventral, 10°8 mm.: antero-posterior, 
14°1; sectional, 4-9. 
It has not been dredged alive or with united valves, and 
one cannot be certain about its left valve. 
It closely resembles 7'. myodorovides, of Smith, but is 
more ventricose, has a concave post-dorsal border, and is much 
more validly concentrically ribbed. 
Habitat.—23 fathoms, Backstairs Passage. 
Ex ppl OVhracia lincolnensis, nu. sp. Pl. xxviii., figs. 19, 20, 21. 13 
Shell, thin, white, elongate-oval; anterior-dorsal border 
nearly straight, scarcely convex ; posterior cancave; ventral 
border almost straight in the posterior half, arcuately ascend- 
ing in the anterior. Anterior end attenuately rounded, pos- 
terior end vertically, straightly truncate; superior and in- 
ferior posterior angles rounded. Right valve slightly more 
convex than the left, which is included all round except at 
the posterior end. Quite obsolete, flat, irregular concentric 
ribs, with very faint miscoscopic concentric striz. The right 
valve has a groove inside its dorsal margin, except at the 
umbo, to receive the left valve, and the inner edge of the 
groove projects to form lamellar teeth, most marked just in 
front of and behind the subumbonal notch. The pallial sinus 
is wide and round, and reaches nearly to the centre of the 
shell. The umbos are acute, incurved, and apposed. 
Dimensions.—Antero-posterior, 73 mm.; umbo-ventral, 
5°1 mm. ; sectional, 3 mm. 
