356 
and each one slightly notches the ventral margin on its outer 
aspect, the notches of successive grooves being more anterior. 
In very young living shells the grooves are very deep at the 
anterior margin, so as to form distinctly projecting lamelle 
here. The prominent prodissoconch is well preserved as a 
tiny concentrically hollowed cap. 
Cuna delta, Tate and May, sp. 
Carditella delta, Tate and May, Trans. Roy. Soc., 8. Austr., 
vol. xxiy., 1900, p. 102. 
Cuna delta, Tate and May, Verco, Trans. Roy. Soc., 8. 
Austr., vol. xxxi., 1907, p. 109. See references there. 
Dredged also in 104 fathoms, thirty-five miles south-west 
off Neptunes, and in 130 fathoms off Cape Jafia, one valve 
at each station. Its habitat is evidently in the shallower 
water, not beyond 22 fathoms. 
Cuna cessens, n. sp. PI. xiv., f. 4 to 7. 
Shell rather thin, trigonal, almost equilateral. Umbonal 
angle rather less than a right angle. Apex capped by a 
minute prodissoconch. Dorsal borders nearly straight, the 
posterior barely excavate, the anterior barely convex. An- 
terior and posterior ventral angles well marked. Ventral 
border convex, not crenulated. Exterior dull, rough, sordid, 
with about ten obsolete radials; and several concentric imbri- 
cations or growth-rests, besides obsolete accremental striation. 
Anterior and posterior sides somewhat excavate into long 
lunule and escutcheon, the posterior more deeply than the 
anterior. The right valve has a large triangular cardinal 
tooth, and a small posterior above and behind the ligamental 
pit. The left valve has a large anterior cardinal, and a 
depression behind the socket of the right wedge tooth for 
the ligament, separated by a tooth, and a small one above 
and behind the pit. Hach valve has a marginal lateral, and 
a lateral separated from the margin by a groove. The in- 
ternal ventral border is not denticulate. The interior is 
white with the ribs and imbrications visible through the 
shell. Colour is a dull light horn tint. 
Dim.—Antero-posterior diameter, 1°8 mm.; umbo-yen- 
tral, 2.1 mm.: sectional, ‘9 mm. 
Dredged in Backstairs Passage, 22 fathoms, several alive 
and valves. 
Diagnosis.—Its closest ally is C. delta, Tate and May; 
but it is less solid, has a wider umbonal angle, has a smaller 
sectional diameter, has the concentric rest gradations, and 
no marginal denticulations. 
Type in Dr. Verco’s collection. 
