1024 PELEOYPODA. [Eulamellibranchia. 



Length. 18 mm. : height. 13 mm. ; diameter of right valve 4 mm., 

 of left valve 1/5 mm. 



Type in my collection. 



Hob. Port Pegasus, Stewart Island, in 12 fathoms (type) ; near 

 (Aivier Island, in 38 fathoms (Captain Bollons). 



Remarks. This species resembles T. lincolnensis, Verco, from South 

 Australia, but the latter is obsoletely concentrically ribbed, the left 

 valve is more convex, and the anterior dorsal margin is not so straight. 



2. Thracia vitrea, Hutton, 1873. Plate 62, fig. 15. 



Li/onsia vitrea, Hutton, C.M.M., 61 ; J. de Conch., xxvi, 44 ; M.N.Z.M., 136. 

 Thracia vitrea, Hutt., P.L.S. N.S.W., ix, 514 ; Plioc. M., 75, pi. 9, f. 80 ; 

 Index, 87. 



Shell moderately large, inequilateral, equi valve, slightly gaping 

 behind, elongately oblong, thin and fragile, truncated posteriorly, 

 concentrically striated, white. Beaks at about the posterior third of 

 length, slightly raised, biangulate posteriorly, acute, directed back- 

 wards. Anterior end longer, convex, the dorsal margin broadly 

 rounded and slowly descending ; -posterior end obliquely truncated, 

 with 2 angular ridges descending from the beak to the upper and 

 lower angle of the truncation on each valve, dorsal margin slightly 

 excavated behind the beaks, thence straight and oblique ; basal 

 margin faintly convex, slightly ascending behind. Sculpture con- 

 sisting of fine concentric lines with occasional periods of rest and very 

 fine microscopic radial striae, producing faint granulation, which is 

 sometimes much more pronounced on the posterior part of the valves. 

 Epidermis very thin, horny, mostly rubbed off. Colour white. In- 

 terior white, dull, sometimes faintly concentrically ridged. Margins 

 smooth, sharp. Hinge without teeth, with spoon-shaped nymphs, 

 which, however, get obsolete in the adult shell ; a flat, oblique litho- 

 desma is present in older shells, grown together with the valves, directed 

 backwards. Ligament external, short. Adductor-scars unequal, super- 

 ficial, the anterior scar very small, the posterior somewhat larger, 

 trigonal. PalUal line distinct, simple, with a deep and broad posterior 

 sinus, extending nearly to the middle, narrowly convex in front. 



Length, 20 mm. ; height, 13 mm. (type). Length, 32 mm. ; height, 

 22 mm. ; diameter, 13 mm. 



Type in the Dominion Museum, Wellington. 



Hob. North Island (Hutton) ; Lyttelton Harbour, in 2 i fathoms 

 (H. S.) ; Stewart Island, in 15 fathoms (A. Hamilton). 



Fossil in the Miocene and Pliocene. 



Fam. PERIPLOMIDJE, Dall. 



Animal with the siphons separate, naked, completely retractile, but 

 not invertible ; monoecious ; marine. 



Shell subnacreous, conspicuously inequivalve, nearly closed, 

 edentulous ; the resilium internal, between 2 anteriorly or vertically 



