138 MACTRID&. 
CG. albida, Zamark, vi., ~. 585; Woodward's Manual of the 
Mollusca, pl. 23, f. 14. Right valve keeled, attached by its anterior 
side ; umbones anterior, sub-spiral; left valve with an oblong curved 
ossicle. 
Length, 2°5. 
Auckland to Cook Strait. Chatham Islands. Australia. Tasmania. 
FAMILY—MACTRID&. 
Labial tentacles long and pointed, pectinated on their inner sides. 
Mantle lobes more or less free beneath, united before and behind, the 
margins more or less distinctly fringed ; siphons united to their extremi- 
ties, which are surrounded by fringes of simple cirri. Foot lanceolate, 
sub-anterior. Shell equivalve. Hinge with two cardinal teeth in each 
valve, the hinder small, compressed, often rudimentary, the front trian- 
gular, more or less deeply notched ; lateral teeth of left valve simple, of 
right valve double; cartilage in an internal triangular pit behind the 
cardinal teeth. Siphonal inflexion distinct. 
Sub-Family—Mactrine. 
Mantle lobes free. Shell sub-triangular, ovate, nearly closed 
behind ; lateral teeth distinct, well developed, laminar. 
Genus, MACTRA —Linneus. 
Hinge with the cardinal teeth moderate; lateral teeth distinct ; 
ligament external, in an oblique, triangular groove opening into the 
upper edge of the cartilage pit ; pallial sinus angular. 
M. discors, Gray, Mag. Nat. Hist., 1837, p. 371 5 Reeve, Conch. 
Ie. f- 17; Voy. Erebus and Terror, pl. 2, f. 4. Shell rotundately ovate, 
somewhat triangular, rather thick, equilateral, regularly convex, smooth, 
greyish-white, covered towards the margin with a blackish-brown epi- 
dermis; posterior side rather flattened, surrounded with a slightly 
keeled obtuse angle ; umbones smail, closely approximated ; lunule and 
area plicately striated ; sinus of the mantle very short, broad, and semi- 
circular (Reeve.) | 
Auckland to Dunedin. 
M. murchisoni, Deshayes, P.Z.S., 1854; Reeve, Conch. Lc., f. 76. 
Shell ovate, sub-ventricose, rather solid, white, smooth, covered towards 
the margin with a straw-coloured epidermis, nearly equilateral, anterior 
side rounded, posterior rather the longer, slightly angularly produced; 
angle linearly keeled ; lunule very large, wrinkle ridged ; umbones close 
set (Reeve.) 
Apparently a younger specimen of the last. 
M. scalpellum, Deshayes, P.Z.S., 1854; Reeve, Conch. Ic, f. 
106; D. pusilla, Hutton, C.M.M., p. 64. Shell triangularly oblong, 
thin, very compressed, equilateral, smooth, shining white; extremities 
