970 PELECYPODA. [EuMmellibrancMa. 



more or less vermiculate ; pallial sinus deep, narrow, pointed ; 

 siphonal gape small ; ligament submerged except at the anterior 

 end, set off by a shelly ridge which roofs the apex of the pit and 

 partially supports the posterior arm of the cardinal tooth ; dental 

 armature concentrated ; chondrophore large ; left cardinal small, 

 its posterior arm shorter, with a small accessory lamella above, both 

 projecting over the pit ; right cardinal with the arms coalescent 

 above, the anterior large, superposed on a feeble anterior lateral, the 

 posterior arm much shorter, projecting over the pit ; a single an- 

 terior and posterior lateral in each valve, but no paired laminae. 



Distribution. Each shore of America. Japan, China, Senegal, New 

 Zealand. 



Fossil in the Miocene and Pliocene. 



1. Raeta perspicua, Hutton, 1873. Plate 60, fig. 5. 



Raeta perspicua, Hutton, C.M.M., 65 ; J. de Conch., xxvi, 46 ; M.N.Z.M., 

 141 ; P.L.S. N.S.W., ix, 518 ; Index, 90. 



Ovate, ventricose and rounded in front, compressed and subangular 

 behind ; umbones posterior, turned forwards, with broad rounded 

 concentric corrugations that show in the interior, and crossed by 

 fine undulating transverse stria?. Yellowish-white. (Hutton.) 



Length, 70 mm. ; height, 50 mm. 



Type in the Dominion Museum, Wellington ; one valve. 



Hob. Bay of Islands. It is said to have been found also at 

 Waikanae Beach, Cook Strait. 



I have never been able to get a specimen. 



Subfam. ZENATIIN.K 



Shell inequilateral, compressed, thin ; hinge concentrated, irregular, 

 the laterals tending to become obsolete or absent ; chondrophore 

 bent out of the plane of the hinge-plate, and more or less adherent 

 to the valve. 



Siphons contractile, naked ; ventral opening of the mantle and 



foot variable. 



KEY TO GENERA. 



A. Anterior end very short, rounded ; shell siliquiform : below the 



cardinals an obscure thickened ray, not extending to the pallial 



line . . . . . . . ZEXATIA. 



B. Anterior end slightly longer than the posterior, rostrate ; shell 



lanceolate ; with 2 internal thickened radiate ribs, extending to 



the pallial line . . . . . . . . KESANIA. 



Genus 1. ZEXATIA, Gray, 1852. 



'/,< nntia, Gray, A.M.N.H. (2), x, 1852, 43. Type : Z. zelandica, Gray = 

 acinaces, Q. & G. Zenutia, Dall, Trans. Wagn. Free Inst., iii, pt. 4, 888. 

 Metabola, C. Mayer, 1867. 



Shell inequilateral, thin, compressed, 'siliquiform, smooth, with a 

 conspicuous epidermis ; dorsal area obscure ; beaks inconspicuous, 



