958 PELECYPODA. \_Eulamdlibranchia. 



Beaks at the posterior third of length, approximate, not prominent, 

 slightly directed backwards. Anterior end much longer, produced, 

 rounded, the dorsal margin long and straight, gently descending ; 

 posterior end straight above, lightly convex below, rapidly descending, 

 subangled towards the basal margin, which is very little convex be- 

 hind, but regularly arched towards the anterior margin. Escutcheon 

 broad, well limited by a keel on each side, descending from the beaks 

 in the direction of the posterior angle of the valves. Sculpture con- 

 sisting of irregular concentric strife, more distinct at the anterior end 

 and finely lamellate on the lower part of the escutcheon ; faint radiate 

 striae are present. Epidermis thin, horny, polished. Colour fuscous- 

 white. Interior white, porcellanous, polished outside the pallial line, 

 with a number of rays directed from the beaks towards the base. 

 Margins with faint radiate striae inside. Hinge-plate massive, tri- 

 angular ; right valve with a very thin oblique cardinal in front of 

 the resilifer, and 2 elongate lateral teeth in front, the lower of which is 

 stronger and raised at both ends, 2 shorter lateral teeth behind the 

 resilifer, the lower triangular, stout, very little oblique, the upper 

 small ; left valve with 1 high lamellar oblique cardinal, 1 slender 

 elongated anterior and 1 stout triangular posterior lateral ; the 

 resilifer central, spoon-shaped, its posterior margin raised. Liga- 

 ment very small, amphidetic, external. Adductor-scars : The anterior 

 scar is pyriforrn, well impressed ; the posterior scar roundish, less 

 deep. Pallial line far removed from the margin, the sinus rather 

 small, broadly rounded, and slightly ascending. 



Length. 47 mm. ; height, 31 mm. ; diameter, 14 mm. (usual size) 

 Length, 74 mm. ; height, 50 mm. ; diameter, 21 mm. (large form). 



Type in the British Museum. 



Hab. North and South Islands, between tide-marks ; more com- 

 mon in the South. Chatham Islands ; Kermadec Islands (Captain 

 Bollons). 



Remark. This mollusc is much used as food by the Maoris and 

 white people. 



Maori. Tua-tua (teste Hutton) ; kahitua (teste Captain Bollons). 

 .wil, in the Miocene and Pliocene. 



Subgen. 2. TARIA, Gray, 1853. 

 Tarn,, (ir f i\, A.M.N.H., 1853, 44. Type : Mesodesma ventricosurn, Gray. 



Shell subtrigonal, subequilateral, the hinge concentrated ; the 

 laterals smooth, subequal, short ; the ligament short, strong, mostly 

 internal ; the resilium narrow ; chondrophore depressed, projecting 

 prominently downward ; pallial sinus well marked, sometimes deep. 



Distribution. New Zealand and the eastern coast of South 

 America. 



