92 yp: Mey 
27-DFI1G 108 
xassatelte; producta,adp. nov. Pl. i., fig 2. 
Shell compressed, solid, ovately-trapezoidal, equivalvular, in- 
equilateral. Umbos conspicuous, acute, apposed, very slightly 
retroflected. Post-dorsal margin gently sloping, concave for one- 
fifth of its length next to the umbo, then almost straight ; front 
dorsal margin scarcely convex, rapidly descending. Ventral 
margin nearly parallel with the post-dorsal, slightly approximat- 
ing behind, uniformly subconvex, regularly rapidly curving up- 
wards to form an almost circular anterior extremity ; slightly 
ascending to join at a rounded angle the posterior margin. ‘This 
is straightly truncated, nearly as long as the post-dorsal line in 
young specimens, about three-fourths in old ones, joining it at an 
obtuse angle of about 120°. Lunule long linear-lanceolate, smooth 
bevelled edges; right valve slightly including left; escutcheon, 
from the umbo almost the whole length of the post-dorsal margin, 
lanceolate, twice as wide as lunule, concave sides, sublenticular 
longitudinal strix, left valve slightly overlapping the right. 
Well-marked post umbonal ridge to postero-ventral angle ; sur- 
face flat behind it, subconvex elsewhere; markedly concentri- 
cally sulcated, seven ridges in the last five lines from the ventral 
margin, stout, acutely rounded, smooth (but for few microscopic 
incised lines, especially on their ventral sides), about equal in 
width to the interstices, which contain from one to three thread- 
lets ; straight behind the umbonal ridge and nearly parallel with 
the margin of the truncated posterior end, but with the angle at 
the ridge more open and rounded in the earlier ridges. Inter- 
nally: right valve, triangular cartilage pit behind a single narrow 
triangular tooth, with a shallow triangular notch in it ; lateral 
teeth, anteriorly a long linear furrow, the inner plate slightly 
iia Saal projecting anteriorly, posteriorly the base of the 
escutcheon scarcely projecting and sharp; left valve, two car- 
dinal teeth, diverging, anterior triangular stout and prominent 
with a long shallow triangular groove, posterior thin and lamellar ; 
lateral teeth, anteriorly base of lunule slightly projecting and 
sharp, posteriorly a long linear furrow, inner plate slightly tri- 
angularly projecting at the posterior part. Ventral margin finely 
denticulated about half a line within the extreme edge, more 
minutely towards front lateral tooth, posterior truncated margin 
smooth. Ornament, light terra-cotta outside, deeper colored at 
_ the umbo, some specimens with many pink radiating lines of 
varying width from umbo to margin, and growing wider; some 
individuals pure white. Internally smooth, shining, white to 
deep flesh tint. | 
Dimensions, antero-post diameter, 10:25 mm.; umbo-ventral, 
7-75; post-dorsal margin, 5-75; posterior, 3:5; depth of closed 
valves, 3:25. 


