PECTFNCULUS. 339 



L. 10506. Several casts, presumably of this species ; from 

 Akuakua (upper beds). Sir James Sector Coll. 



L. 10508. Casts of typical examples; from Akuakua (lower 

 beds). Sir James Hector Coll. 



L. 10510. Example of the right valve ; from Taipos. 



Sir James Hector Coll. 



CucuUsea wortliingtoni, Hutton. 



1873. Cuculkea tvorfhingtoni, Hutton, Cat. Tert. Moll. N.Z. p. 27. 



" Ventricose, much larger than high; posterior side produced, 

 rather dilated ; umbones distant ; hinge at right angles to the 

 axis of the shell." — Mutton. 



It is difficult to satisfactorily determine specimens from such 

 a meagre description, but that alluded to below is probably refer- 

 able to this species. 



Dimensions. — Height 66 mm. ; length 87 mm. 



Form, and Loc. — Pliocene (?) : Parimoa, New Zealand. 



L. 10445. Left valve of the adult. W. B. D. Mantell Coll. 



Genus PECTUNCULUS, Lamarck. 

 [Mem. Soc. Hist. Nat. Paris, 1799, p. 87.] 



This differs fi'om Cucullcea, in being orbicular, or suborbicular, 

 equivalve and almost equilateral ; the umbones are closer together, 

 and the area is, in consequence, narrower and relatively smaller. 

 The ligamental area, which is external, carries diverging grooves ; 

 cardinal border semicircular ; teeth prominent, strong, becoming 

 obliterated uuder the umbones as the gerontic stage is approached, 

 by the invasion of the ligamental area ; margins of the valves 

 crenulated. 



Type. — Area peciunculus, Linnaeus. 



