850 PELECYPODA. [Filibranchia. 



Sect. 1. BATHYARCA, Kobelt, 1891. 



Balhyarca, Kobelt, Conch. Cab., ed. 2, viii, Area, 1891, 213. Type : 

 Area pectunculoides, Scachi. 



Shell small, usually abyssal, inflated, with prosogyrate beaks and 

 a rather narrow but long furrowed area, the hinge-margin nearly or 

 quite as long as the shell ; teeth few, oblique, in two series, often 

 separated by a wide gap in the centre ; the right valve smaller, the 

 sculpture of the two valves often very discrepant ; epidermis usually 

 imbricated. 



Fossil from the Eocene. 



3. Area cybaea, Hedley, 1906. Plate 51, figs. 7, la. 



Bathyarca cybcea, Hedley, T.N.Z.I., xxxviii, 1905 (1906), 71, pi. 1, f. 3, 4. 

 Area (Bathyarca) cybcea, Suter, T.N.Z.I., xl, 353. 



Shell small, oblong, short and inflated, inequivalve, a little in- 

 equilateral without impressed ray, posteriorly and anteriorly rounded, 

 sinuate beneath the beak. Beaks much inrolled, at a third of the 

 length of the shell. Ligamental area narrow. Sculpture finely reti- 

 culate ; a series of delicate .subequal evenly spaced riblets radiate 

 from the umbo to the margin ; as growth proceeds new riblets are 

 intercalated till about 50 reach the margin ; the radiate radii are 

 broken into short lengths by concentric growth-lines which produce 

 minute prickles at the point of intersection. Epidermis very light 

 brown, thin, very easily peeling oft'. Colour light brown, white when 

 devoid of epidermis. Interior rayed by imprint of external sculpture, 

 white, lightly sinning. Margins finely crenulate within, except at 

 byssal gape. Hinge-plate edentulous under the beaks, posteriorly 

 with 4 nearly horizontal, anteriorly with 4 highly inclined small teeth. 



Length, 3 mm. ; height, 2-15 mm. ; diameter, 2 mm; (type). 



Type in the Dominion Museum, Wellington. 



Hab. Off Great Barrier Island, in 110 fathoms ; near Cuvier 

 Island, in 38 fathoms (Captain Bollons) ; off Lyttelton, in 100 fathoms 

 (E. R. Waite) ; near the Snares, in 50 fathoms (Captain Bollons). 



Remarks. Tin's species is nearest allied to the Australian B. per- 

 versidens, Hedley, from which it differs by the less development of 

 the posterior side. (Hedley.) 



Genus 2. GLYCYMERIS, Da Costa, 1778. 



Glycymeris, Da Costa, Brit. Conch., 1778, 168. Type : Area tjlycymeris, L. 

 Tuceta, Bolten, 1798. Axinaca and Axinceoderma, Poll, 1791. Pectun- 

 culus, Lamarck, 1799. Not Glycymeris, Lamarck 1799. 



Animal with the mantle open throughout ; foot without byssus, 

 but with a plantar surface ; the heart traversed by the rectum. 



Shell orbicular or suborbicular, equivalve, equilateral or nearly 

 so, convex, solid and thick, inside porcellanous, with a velvety epi- 

 dermis on the outside ; beaks slightly curved inward, nearly straight ; 



