PELECYPODA. 1009 



distribution it shares with several other bivalves viz., Area reticulata, 

 Lima lima, Carditacalyculata, Venericard.iacorbis, Thyasira flexuosa, &c. 

 Fossil in Great Britain, dating back to the Coralline Crag. 



Section 2. ALOIDIS, Megerle, 1811. 



Aloidis, Megerle von Muehlfeldt, Entw., 1811, 67. Type : Corbula sulcata, 

 Lamarck. 



Like Corbula, but with strong concentric sculpture and keeled 

 rostrum. 



KEY TO SPECIES. 



A. Valves rather thin, dorsal and posterior margins usually pink colour macilenta. 



B. Valves very thick and solid, more ventricose, colour yellowish-grey zdandica. 



'2. Corbula macilenta, Hutton, 1873. Plate 55, figs. 3. a. 



Corbula macilenta, Hutton, C. Tert. M., 18 ; Suter, T. N.Z.I., xxxviii, 319. 

 C. erythrodon, Lamarck : Hutton, J. de Conch., xxvi, 44 ; M.N.Z.M., 

 135 ; P.L.S. N.S.W., ix, 513 ; Index, 88 ; not of Lamarck. C. pura, 

 Webster, T.N.Z.I., xxxvii, 1904 (1905), 279, pi. 10, f. 12. 



Shell small, oblong, subtrigonal, inequivalve and inequilateral, 

 rather thin, sharply angled behind, concentrically striated, white with 

 pink on the dorsal and posterior margins. Beaks somewhat raised, 

 that of the right valve a little higher, approximate, directed forwards, 

 with a distinct anterior and posterior keel. Anterior end shorter, 

 narrowly convex, the dorsal margin a little excavated in front of 

 the umboues, descending ; posterior end obliquely truncated, sharply 

 angled below, the dorsal margin straight, oblique ; basal margin 

 broadly convex. Lunule not distinctly defined. Escutcheon long 

 and rather broad, elliptical, limited by keels descending from the 

 beaks towards the posterior angle, with a median ridge on the right 

 valve. Sculpture consisting of somewhat distant sharp concentric 

 ribs, the interstices with microscopic concentric and radial fine lines ; 

 the sculpture is usually more pronounced on the left valve. Colour 

 dirty-white, the dorsal and posterior margins usually pinkish. Interior 

 white above and behind pink. Margins smooth, thin, and sharp, 

 that of the right valve advancing a little over the left. Hinge : Right 

 valve with a small subumbonal tooth, slightly turned upward ; left 

 valve with a horizontal process and a small posterior tubercle, a deep 

 socket in front. Ligament small, internal. Adductor -scars large, sub- 

 equal. Pallial line distinct, entire. 



Length, 13 mm. ; height, 7-5 mm. ; diameter, 5 mm. (type). 



Type, from the Pliocene, in the Dominion Museum, Wellington. 



Hob. North Island : Auckland Harbour ; near Channel Island. 

 Hauraki Gulf, in 25 fathoms ; near Cuvier Island, in 38 fathoms 

 (Captain Bollons) ; Titahi Bay, Cook Strait (Miss Mestayer). 



Fossil in the Pliocene. 



