BY C. HEDLEY. 681 



each valve are twelve. The scales are suppressed near the byssus- 

 exit. Teeth eighteen, of which seven are posterior, increasing 

 in size and inclination as they recede from the centre. Length, 

 15; height, 7; breadth of conjoined valves, 7 mm. 



This species is common under stones at low tide-level in the 

 Hormosira-zone, all along the coast of New South Wales. It has 

 hitherto lacked a name through misidentification with a Peruvian 

 species. A member of the subgenus Acar, it nearest approaches 

 the tropical A. plicafa Dillwyn (founded on Chemnitz, Conch. 

 Cab., xi., PI. 204, fig.2008). From that, it is distinguishable by 

 finer sculpture, especially by the smaller and more numerous 

 radials of the antero-superior face, by shorter broader form, and 

 by far smaller size. Compared with the Adelaidean Area lami- 

 nata Angas,* it is smaller, more compac*', and delicately sculp- 

 tured. 



Arca metella, sp.nov. 

 (Plate li., figs.36, 37.) 



Shell small, rather thin, inflated, oblique, medially constricted, 

 especially in the young, and in the left valve. Colour dull 

 white. Anterior margin obliquely truncate, projecting past the 

 hinge-line. Ventral margin insinuate, ascending posteriorly till 

 it meets the hinge-line at a right angle. Umbo at one-third of 

 the total length from the posterior end, low and slightly project- 

 ing over the area. Fine, close, radial threads, about seventy in 

 number, are crossed by similar threads about thirty in number, 

 and develop a bead at the point of intersection. Ligamental 

 area narrow-lanceolate, from the umbo a few oblique furrows 

 cross the area anteriorly. The hinge has seven posterior and 

 ten anterior teeth; those I'emote from the centre are inclined. 

 Length, 10; height, 5-5; depth of single valve, 3 mm. 



Numerous separate valves, associated with Arca strabo, were 

 dredged by myself in 100 fathoms off Wollongong, and in 80 

 fathoms off Narrabeen, N. S. Wales. 



* Barhatia laminata Angas, Proc. Zool. Soc, 1865, p. 655. t^Arca 

 irudina Lamarck, An. s. vert., vi., 1819, p.41; Lamy, Journ. de Conch., 

 Iv., p. 80. 



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