196 
Accremental strie irregular in distance and size mark the 
surface, and form rude flat concentric ridges at intervals. 
Well-marked radial strie cover all the posterior half of the 
shell, extending from the umbo to the ventral border, some- 
what interrupted at the edges of the concentric ridges; these 
. are quite absent from the anterior half. 
Dim.—Antero-posterior diameter, 89 mm.; umbo-ven- 
tral, 5°2; sectional of one valve, 3°5 mm. 
Locality.—Cape Jaffa, 130 fathoms, one valve. 
scapha, n. sp. PI. xii., figs. 1 to 5. Efe 
Shell small, solid, white, oval. Umbos terminal, round, 
inflated, directed slightly forward, approximate but not in 
contact. Prodissoconch very distinct, separated definitely 
from the dissoconch by a fine groove; its earliest third is quite 
smooth, its later two-thirds engraved with concentric lines, 
gradually growing more valid. _Post-dorsal border nearly 
straight for 17 mm., forming an open rounded angle with - 
the posterior border, which is nearly straight for 1‘7 mm., then 
sweeps with a slight convexity into the short-curved, circular, 
ventral border. The anterior dorsal border.is very short, al- 
most entirely under the umbo. The antero-ventral border is 
slightly convex. The whole dorsum is engraved with crowded, 
slightly-curved, radial lines, latticed by concentric lines nearly 
as valid; some of the latter at distant intervals in the early 
stages of growth are much deeper, so as to form slightly imbri- 
cating ledges. The inner margin of the shell has fine denti- 
culations from the end of the post-dorsal border all round 
and almost to the central extremity of the anterior dorsal 
border under the umbo; they do not reach the outer edge of 
the shell. The straight edge of the prodissoconch is set some- 
what obliquely to the anterior dorsal border, the central ex- 
tremity of which extends slightly behind the centre of the 
edge of the prodissoconch. The post-dorsal line is provided 
with many (more than 20) close-set, low, vertical teeth on its 
inner surface. Beneath them is the scar of the ligament for 
the anterior three-fourths of their extent, somewhat increas- 
ing in width posteriorly, and having a rounded end. It seems 
to pass out between the prodissoconch and the anterior dor- 
sal hinge-line to become external. The anterior dorsal bor- 
der has a few denticulations and one tooth, and is supported 
by a sort of thickening which projects slightly into the cavity 
of the shell and has a rounded central end. Two elongated 
muscle-scars occupy the middle third of the sides of the shell, 
not far from the margin, narrowing dorsally ; the posterior is 
rather the larger. 
