346 
dorsal area transversely elongate, narrowly triangular. An- 
terior dorso-lateral angle obtuse, about 135 deg.; posterior 
about 100 deg. Anterior border slightly concave for about 
one-fourth of its length, then uniformly slightly convex. 
Posterior border much shorter, at first sub-concave, then 
nearly straight. Ventral border semicircular, joining the 
anterior border with a more open sweep than the posterior. 
Surface convex; with sixteen radial ribs, smooth, rounded, 
nearly as wide as the interspaces, with several intercalated 
riblets. Concentric striae granulate the intercostal spaces, and 
form sublenticular costule on the sides, more marked on the 
anterior, near the dorsal border. 
- The cartilage-pit is sub-central, and triangular crossing 
the dorsal area to the umbo, concave. Hinge-plate narrow 
near the pit, widest at the angles; teeth about seven on each 
side, diverging, extending slightly along the lateral borders. 
Interior slightly furrowed by the ribs. Ventral border 
squarely denticulated. 
Dim.—Umbo-ventral diameter, 3°55 mm.; 3°7 mm., in- 
cluding the umbo; antero-posterior, 3 mm. 
Hab.—Type locality, 104 fathoms, 35 miles south-west 
of Neptune Islands, 40 valves; 90 fathoms off Cape Jaffa, 1 
valve. 
Type in Dr. Verco’s collection. 
Mytilicardia crassicosta, Lamarck. Kesh ry 
Cardita crassicosta, Lamarck, Anim. 8. Vert., 1819, vol. vi., 
pt. 1, p. 24, No. 13. 
Cardita citrina, Lamarck, op. cit., p. 637, No. 21. 
Cardita crassicostata, Reeve; Conch. Icon., 1848, vol. i., pl. 2, 
Bes 15 (2h) Udy ed hy . 
Cardita tridacnoides, Menke; Moll. Nov. Holl., 1843, p. 39, 
No. 222. 
Dredged alive at all depths from 8 fathoms to 24, in 
both Gulfs and Straits. Very young individuals have been 
taken alive in 45 fathoms off Beachport and east of the 
Neptunes, and in 55 fathoms off Cape Borda. Small valves 
occur in numbers in 100 and 110 fathoms off Beachport, and 
in 130 fathoms off Cape Jaffa. It would appear as if very 
few mature shells are found above 15 fathoms, though the 
range of the smaller individuals extends to over 50 fathoms. 
Some small specimens are of a uniform rosy-pink colour ; 
others have the dorsal two-thirds of the posterior half of a 
very dark-brown internally. The ventral border may be 
quite straight, or very deeply excavate in front of its centre. 
There may be a sort of dorsal fin just in front of the posterior- 
dorsal angle, due to expansion of a radial rib. The shell may 
be elongate transversely and low umbo-ventrally, or short 
