Thyasira.} PELECYPODA. 919 



1. Thyasira flexuosa, Montagu, 1803. Plate 63, fig. 11. 



Venus sinuosa, Donovan, Nat. Hist. Brit. Sh., 1801, pi. 12, f. 2 ; not of 

 Pennant, 1777. Tellina flexuosa, Montagu, Test. Brit,, 1803, 72. Amphi- 

 desmn flexuosa, Lamarck, A.s.V., v, 1818, 492. Lucina sinuata, Lamarck, 

 op. cit., v, 1818, 543 : Hanley, Cat. KIM.-. Biv. Shells, 1844, 77. Ptychina 

 hi/>h'cata, Philippi, En. Moll. Sicil., i, 183(5, 15 : ii, 1844, 4. Lucina sinuosa, 

 Thorpe, Brit. Man. Conch., 1844. 74 ; not of Romer. Cri/ptodon bisinu- 

 atus, S. Wood, A.M.N.H., vi, 1840, 247. Axinus sinuatus, Philippi, 

 Zeitschr. Malak., 1845, 91. Cn/plodon sp., Mutton, C.M.M., 75. Axinus 

 flexuosus, Mont. : Fischer, Man. Conch., pi. 19, f. 7. Cri/ptodon flexuosus, 

 Mont,, Chall. Rep., xiii, 192. Li-hin flexuosa. Mont. : Forbes and 

 Hanley, Brit. Moll., ii, 54, pi. 35, f. 4. Thi/asini /lc.n<o*ri, Mont. : Call. 

 Trans'. Wagn. Free Inst., iii, pt, (i, 1339 ; Hedley, T.N.Z.I., xxxviii. 

 1900, 74. 



Shell delicate and fragile, inequilateral, suborbicular, with a pos- 

 terior sulcus, convex, pellucid, white, smooth. Beaks rather pro- 

 minent, small and acute, inclined forwards. Anterior end smaller 

 and narrower than the posterior, the front dorsal edge sloping down- 

 wards, slightly excavated in front of the beaks ; posterior end 

 angularly produced, the dorsal margin oblique, straight, lightly 

 angled on meeting the convex posterior margin, which has a distinct 

 sinus at the termination of the furrow extending from the apex ; basal 

 margin convex. There is a faint roundish lunular impression in 

 front of the umbones. Sculpture consisting of irregular concentric- 

 wrinkles. Colour white. Interior white, shining, radially striated. 

 Margins smooth, sharp. Hinge-line narrow, angular, the right valve 

 with an erect pseudo-tooth below the beak. Ligament moderately 

 long, but little visible from the outside, nymphse not much developed. 

 Adductor-scars elongate, the anterior impression double. Pallial line 

 simple. 



Diameter Ant.-post., 19mm.; dorso-ventral, 17mm.: thick- 

 ness, 13-5 mm. 



Type in the British Museum. 



// a &. Off Great Barrier Island, in 110 fathoms ; Waikanae Beach, 

 Cook Strait ; Wet Jacket Arm, Dusky Sound, in 12 fathoms ; Port 

 Pegasus, Stewart Island, in 18 fathoms (Captain Bollons). Also 

 Australia, northern Europe, North Atlantic south to the Canaries 

 and Azores, Mediterranean, north-east North America, in 2 to 500 

 fathoms. 



Fossil in the European Neocene and Pleistocene. 



'2. Thyasira otagoensis, n. sp. Plate 53, fig. 8. 



Shell small, orbicular, slightly ventricose, inequilateral, with a 

 feeble posterior fold, thin and pellucid, smooth, whitish. Beaks 

 prominent, convex, inclined forward, approximate. Anterior end 

 produced, considerably longer than the posterior end, semicircular, 

 the dorsal margin slowly descending, basal margin regularly curved ; 

 posterior end short, regularly convex, with a slight excavation at the 

 terminus of the feeble fold descending from the beaks. Sculpture 



