1012 PELECYPODA. [Eulamdlibranchia. 



Shell small, irregular, very inequilateral, the young with a single 

 cardinal tooth under the beak in each valve, the adult with the teeth 

 obsolete ; ligament external, more or less prominent. Muscular im- 

 pressions strong, wide apart ; pallial line interrupted, sinuated pos- 

 teriorly. 



Distribution. Universal in the temperate and colder seas. 



Fossil in the Tertiary. 



Vernacular Name. Rock-borer. 



1. Saxicava arctica, Linne, 1767. Plate 55, figs. 6, a. 



Mi/a arctica, L., Syst. Nat., cd. 12, 1767, 1113. Saxicava arctica, L., C.M.M., 

 60 ; Grit. List, 41 ; Chall. Rep., xiii, 78 ; Index, 88. Solen minutus, L., 

 op. tit., 1115. Saxicava rugosa, Lamarck, A.s.V., v, 1818, 501. Corbula 

 australis, Lamarck, op. cit., 495. Saxicava australis, Lam., M.N.Z.M., 

 134; Button, P.L.S. N.S.W., ix, 513. S. spinifera, Sowerby, Conch. 

 Icon., xx, f. 12. There are many more synonyms. 



Shell small, polymorphous, inequilateral, usually oblong, very 

 rugose, thin, sometimes fragile, young specimens very often with 

 posterior spinous ridges, white or light brown. Beaks approximate, 

 slightly raised, tumid, tricarinate, 1 anterior and 2 posterior, incurved 

 and acute. Anterior end much shorter, usually truncated or convex 

 and very rapidly descending ; posterior end frequently very long, 

 truncated or convex ; the basal margin broadly convex or more or 

 less deeply sinuated. Epidermis thin, dull, brown. Sculpture con- 

 sisting of very irregular, concentric, sharply raised, often anastomosing 

 riblets, crowded in front, distant and rather lamellar posteriorly ; 

 2 sharp ridges are descending on each valve from the umbones towards 

 the posterior end, and in young specimens are usually ornamented 

 with small tubular spines. Colour light brown or nearly white. 

 Interior white, slightly shining, smooth. Hinge very narrow ; right 

 valve with an oblique small tooth below and just in front of the urnbo, 

 and a socket behind it ; left valve with a small, conical, upturned 

 tooth a little behind the beak. Ligament external, short, rather pro- 

 minent. Adductor-scars unequal, the posterior larger. Pallial sinus 

 shallow. 



Dimensions extremely variable, the greatest length of shells I 

 have seen being 17 mm. 



Hob. Throughout New Zealand, Chatham, Auckland, and Ker- 

 madec Islands. 



The species is apparently distributed all over the globe, and is 

 found from low-water mark to about 500 fathoms. 



Fossil in the Pliocene. 



Genus 2. PANOPEA, Menard, 1807. 



Panopea, Menard, Annales du Mus., Paris, ix, 1807, 135. Type : Mya ;;///- 

 cymeris, Born. Glycimeris, Lamarck, 1799. Panopia, Swainson, 1840. 



Animal with long siphons, united as far as their extremities, and 

 invested with a thick, wrinkled epidermis ; pedal orifice small ; foot 



