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 costulae 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, 3'5 mm.; 3*7 mm., in- 

 cluding the umbo : antero-posterior, 3 mm. 



Hah. — 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, Lannrck. 



Cardita crassicosta, Lamarck, Anim. S. Vert., 1819, vol. vi., 

 pt. 1, p. 24, No. 13. 



Cardita citrina, Lamarck, op. cit., p. 637, No. 21. 



Cardita crassicostata, Reeve; Conch. Icon., 1843, vol. i., pi. 2, 

 f. 7, a, h, c, d, e. 



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 



