Mrtc1nt.\ PELECYPODA. 967 



lamellar, close to the dorsal margin and parallel with it ; the lateral 

 laminae short, triangularly raised ; left valve with a stout high tri- 

 angular cardinal and a short obsolete tooth behind and above it, an 

 accessory anterior lamella coalescent with the anterior lateral tooth, 

 which is short and triangularly raised ; resilifer large, oblique, roofed 

 apically. Ligament short and narrow, very little of it visible externally, 

 the greater part of it above the upper posterior part of the resilifer. 

 Adductor-scars unequal, rather small, the anterior pyriform, the 

 posterior roundish. Pallial sinus rather broad, ascending, narrowly 

 rounded in front, extending nearly half across the disc. 



Length, 73 mm. ; height, 56mm. (type). Length, 85mm. ; height, 

 66 mm. ; diameter, 44 mm. 



Type in the British Museum. 



Hab. West coast of the North Island (Dr. Dieifenbach). North 

 and South Islands, in deep mud, estuaries, and by the side of tidal 

 channels. 



Fossil in the Pliocene. 



5. Mactra rudis, Huttou, 1873. 



Mactra rudis, Hutton, C. Tert. M., 19 ; Plioc. M., 77, pi. 8, f. 83 ; Index, 90. 



Shell suborbicular, thin, compressed, and rather sinuated ; rudely 

 concentrically striated. Anterior side rather shorter, its dorsal margin 

 straight. Posterior dorsal margin arched. Anterior lateral tooth of 

 the left valve short and high. Lower margin irregular in outline. 

 Pallial sinus deep, rather descending, rounded at the apex. (Hutton.) 



Height, 60mm. ; length, 60mm. (type). Height, 43mm. ; length, 

 53 mm. (specimen figured by Hutton). 



Type, from the Pliocene, in the Dominion Museum, Wellington. 



Hab. Whangaroa Harbour (Professor Thomas). 



Fossil in the Pliocene. 



Genus 2. SPISULA, Gray, 1837. 



Spisula, Gray, A.M.N.H., i, 1837, 337, 372; Dall, "Nautilus," viii, 1894, 20, 

 40 ; P. Mai. S., i, 211 ; Trans. Wagn. Free Inst., iii, pt. 4, 878. Type : 

 Mactra solida (L.), Gray. 



Shell small, subequilateral, trigonal, with a thin epidermis, adjacent 

 beaks, and concentrically grooved dorsal areas ; pallia! sinus small, 

 rounded ; gape obsolete ; valves convex ; ligament saggitate, set in 

 a callous area close to the dorsal margin and not set off from the 

 chondrophore by any shelly ridge ; dental armature normal, strong, 

 not concentrated ; the opposed surfaces of the laterals transversely 

 grooved ; left cardinal small, prominent, with a small posterior ac- 

 cessory lamella, the posterior ends of both projecting over the chon- 

 drophore ; right cardinal with the arms coalescent above, the anterior 

 arm close to the dorsal shell-margin ; hinge-plate thick and flattish ; 

 exterior smooth or concentrically striated ; the dorsal areas ill de- 

 fined. (Dall.) 



