1008 PELECYPODA. [Eulamellibranchia. 



Sect. 1. CORBULA, s. str. 

 Type : C. gallica, Lamarck. Bicorbula, Fischer, 1887. 



Shell subtrigonal, ligament internal, globose, valves feebly con- 

 centrically sculptured with no rostral keels, sculpture discrepant on 

 the 2 valves. 



1. Corbula gibba, Olivi, 1792. Plate 55, fig. 2. 



Tellina gibba, Olivi, Zool. Adriat., 1792, 101. Mya incequivalvis, Montagu, 

 Test. Brit., 1803, 38, suppl. pi. 26, f. 7. Corbula nucleus, Lamarck. 

 A.s.V. (ed. Desh.), vi, 139: Conch. Icon., ii, pi. 2, f. 10: Forbes and 

 Hanley, Brit. Moll., i, 180, pi. 9, f. 7-12 ; pi. G, f. 3. C. striata, Fleming, 

 Brit. Anim., 425. C. olympica, Costa, Test. Sicil., 27. C. rotundata, 

 Sowerby, Min. Conch., 572. 



Shell more or less triangular, solid, very inequivalve, inequilateral ; 

 the right valve ventricose, overlapping the left at the base and pro- 

 jecting beyond it at the umbones, closely grooved ; the left valve 

 smaller, less ventricose, with fine concentric striae and a few fine 

 radiating lines. Beaks slightly raised, convex, incurved, the right 

 umbo almost resting on the margin of the left valve. Anterior end 

 usually shorter, convex, the dorsal margin straight, sloping ; posterior 

 end more or less produced and rostrate, narrowly truncated, the dorsal 

 margin slightly concave, very slowly descending ; ventral margin 

 more or less arched, more ascending behind. Area excavated in front 

 and behind the umbones. Sculpture : Right valve with 2 low posterior 

 ridges extending from the umbo to the truncation behind, closely 

 concentrically ribbed, the ribs smooth, rounded, the interstices a little 

 narrower, with a few well-marked periods of rest ; left valve almost 

 smooth, with fine concentric lines and distant radiate striae, an indis- 

 tinct ridge running from the beak to the lower end of the rostrum. 

 Epidermis persistent on the left valve only, rather thick, umber-brown. 

 Colour white, brown at the dorsal and ventral margins. Interior 

 almost devoid of colour. Hinge : Eight valve with a strong some- 

 what recurved tooth. Pallial line entire. 



Length, 12 mm. : height, 8 mm. ; diameter, 7 mm. 



Hob. Chatham Islands. 



The species is common in the British seas, coasts of the Continent 

 of Europe, Mediterranean included, ranging in depth from a few to 

 about 70 fathoms. 



Remarks. Professor W. B. Benham kindly lent me the type of 

 Hutton's C. Haastiana, and to Mr. Edgar R. Waite I am indebted for 

 the loan of a perfect specimen labelled by the late Captain Hutton, 

 '' C. Haastiana; locality, Chatham Islands." On comparing the 

 latter specimen with the type I found it to be quite distinct, and, 

 studying the diagnoses of various species of the genus, and looking 

 over the species in my collection, I found the Chatham Island shell 

 to agree in every respect with C. gibba, Olivi. This is the only 

 specimen from New Zealand waters I have seen. The peculiarity of 



