Modiolaria.] PELECYPODA. 8t>9 



the broadly rounded angle running to the posterior end of the basal 

 margin. Anterior end convex, slightly excavated beneath the umbones, 

 the dorsal margin almost straight and horizontal. Posterior end nar- 

 rowly rounded, slightly compressed ; basal margin slightly concave 

 at the posterior third. Sculpture consisting of fine radiate riblets, 

 anteriorly under the beaks, posteriorly from a little in front of the 

 dorsal lateral ridge ; median areas smooth, except for growth-lines. 

 Epidermis thin, shining, yellowish, produced posteriorly into long 

 thin bristles. Colour light yellow. Interior white, iridescent, showing 

 the external sculpture distinctly. Man/ins crenate, but smooth at 

 the base where the byssus passes. Hinije-plate short, crenate, broaden- 

 ing anteriorly. Ligament long, narrow, the greater part internal. 

 Adductor-scars not much impressed. Pallial line continuous, simple. 



Diameter Ant. -post., 10 mm. ; dorso-ventral, 5 mm. : thickness, 

 5 mm. 



Type in the British Museum. 



Hob. North Island : Bay of Islands, Hauraki Gulf. Also Tas- 

 mania and Australia. 



2. Modiolaria impacta, Hermann, 1782. Plate 58, fig. 7. 



Mytilus' irnpCLctus, Hermann, Naturforscher, xvii, 1782, pi. 3, f. 5-8 ; Wood, 

 Index Test., 1825, 59, pi. 12, f. 40. Moditda impacta, Herm. : Hanley, 

 Cat. Rec. Biv. Shells, 241 ; Conch. Icon., x, pi. 9, f. 64. Crenella impacta, 

 Herm., M.N.Z.M., 168. Modiolafia imiiactft, Herm., Conch. Cab., 1889, 

 147, pi. 34, f. 9. Modiola discors, Lamarck. A.s.V., vi, 1819, 114; not 

 of Linne. Crenrlla discors, Lam., C.M.M., 78. Modiolarca im/iai-ln. 

 Herm., Dietf. N.Z., 259. 



Shell fairly large, oval, ventricose, with anterior and posterior 

 strong radial ribs, thin but solid, olive to green and yellow. Beaks 

 nearly terminal, approximate, slightly hooked, rounded, with an 

 indistinct angle running to the posterior end. Anterior end broadly 

 convex, ventricose, dorsal margin convexly raised at the middle. 

 Posterior end narrowly rounded and somewhat produced below ; the 

 basal margin horizontal, lightly convex. Sculpture : A few distant 

 strong and broad radiate ribs, the interstices each with a much narrower 

 rib at the anterior end, and numerous similar ribs at the posterior 

 end, the intermediate area usually devoid of radial sculpture ; the 

 whole surface with concentric growth-lines. Epidermis coriaceous, 

 slightly shining, yellowish-olive. Colour brown, reddish-ash to olive, 

 sometimes yellow at the edge above, and green below. Interior whitish, 

 with concentric purple bands, iridescent, showing the radial sculpture. 

 Margins crenate anteriorly and posteriorly, smooth at the middle of the 

 base. Hinge-plate narrow and short, indistinctly crenate, terminating 

 in a point behind. Ligament rather short, narrow, the greater part 

 internal. Posterior adductor-scar large, round, superficial. Pallial 

 line continuous, simple. 



