Spisula.} PELECYPODA. 969 



2. Spisula aequilateralis, Deshayes, 1854. Plate 60, figs. 4, a. 



Mactra cequilateralis, Desh., P.Z.S., 1853 (1854), 17 ; Ereb. & Ter., 5, pi. 2, 

 f. 10; Button, J. cle Conch., xxvi, 45; M.N.Z.M., 139; T.N.Z.I., xiii, 

 204. M. cequilatera, Desh., Conch. Icon., viii, f. 14 ; C.M.M., 63 ; Crit. 

 List, 44 ; Hutton, P.L.S. N.S.W., ix, 517 ; Index, 90. 



Shell moderately large, solid, trigonal, nearly as high as long, 

 concentrically striated, white, dorsal posterior area flattened and 

 laterally sharply angled. Beaks approximate, bicarinate, incurved, 

 acute. Anterior end subangulated, the dorsal margin rapidly descend- 

 ing, nearly straight ; posterior end somewhat longer, sharply angled, 

 the dorsal margin long, rapidly descending, a little convex ; basal 

 margin broadly regularly arched. Lunular area large, smooth ; pos- 

 terior dorsal area flattened, slightly raised towards the valve-margins, 

 smooth, with a sharp angle on each side, descending from the umbones 

 to the posterior angle below. Epidermis thin, horny, shining, extend- 

 ing beyond the margins, usually lost on the greater part of the shell. 

 Sculpture consisting of concentric striae, raised into sharply rounded 

 riblets on the anterior and ventral parts of the valves ; indistinct 

 distant radial lines are usually visible. Colour greyish-white, the 

 lunule and the central part of the escutcheon light brown, the um- 

 bones purplish. Interior .yellowish - white, porcellanous, polished, 

 faintly radially striate. Margins smooth, thick, sharp. Hinge : 

 Right valve with 2 cardinals, coalescent above, the posterior extending 

 over the resilifer, the anterior close to the dorsal shell-margin ; 2 

 anterior longer and 2 posterior shorter lamellae, which are corrugated 

 on the inner sides ; left valve with a small A -shaped cardinal and an 

 accessory lamella above and behind, which with the posterior arm 

 of the cardinal extends over part of the resilifer ; the latter is large, 

 oblique, and not separated by shelly matter from the ligament, which 

 is short, inset, but visible externally. Adductor-scars subequal, tri- 

 angularly ovate, not deep. Pallial sinus not very large, horizontal, 

 narrowly rounded in front. 



Length, 77 mm. ; height, 60 mm. ; diameter, 38 mm. 



Type in the British Museum. 



Hob. North and South Islands ; commonly found washed up on 

 sandy beaches after gales. 



Fossil in the Pliocene. 



Subfam. P 



Shell subequilateral, nearly closed, thin ; hinge feeble, concen- 



trated, the laterals partly obsolete or much reduced. Siphons wholly 



retractile, naked ; mantle partially closed ventrally. (Dall.) 



Genus 1. RAETA, Gray, 1853. 



Ra'-ta, Gray, A.M.N.H. (2), xi, 1853, 43. Type : Lutraria canaliculata, Say. 

 Rni-td, ball, Trans. Wagn. Free Inst., iii, pt, 4, 882. 



Shell large, inequilateral, thin, inflated, acutely rostrate behind, 

 concentrically plicate ; dorsal areas obscure, the surface of the valves 



