Conieocyclas.] PELECYPODA. 935 



defined by a delicate line. Ligament inset. Hinge consisting of 

 paired laterals, anterior and posterior, in the right valve, and single 

 ones in the left valve, showing sometimes a faint striation or granula- 

 tion ; cardinals 2 in each valve, the posterior left and anterior right 

 slender and entire, the two others thick, subtriangular, and bifid ; 

 in the great majority of species the 2 right cardinals remain con- 

 nected and form a single sinuous or angular tooth. 



The genus has a wide distribution. Found in rivers and lakes 

 to a depth of about 150 fathoms. 



Fossil. Cretaceous and Tertiary. 



Vernacular Name. Pea-shell. 



Subgen. 1. CORNEOCYCLAS, s. str. 



Nepionic shell convex, concentrically striated ; hinge with 2 

 separate cardinals in the left and a single compound, usually arcuate, 

 cardinal in the right valve. 



KEY TO SPECIES. 



a. Shell small, oval ; length, about 3 mni. ; much compressed, 



anterior end elongated . . . . . . . . Hodgkini. 



b. Shell larger, oblique ; length, 56 mm. ; lightly ventricose, 



anterior end elongated . . . . . . . . novce-zelandiw. 



c. Shell small, oval ; length, 3-4 mm. ; somewhat inflated, 



anterior end regularly convex ; right valve with 2 separate 



cardinals . . . . . . . . . . uucklandica. 



Sect. 1. CORNEOCYCLAS, s. str. 

 Type : C. pusilla, Gruel. 



Nepionic valves passing into the mature disc without any strong 

 demarcation ; the anterior cardinal and lateral adjacent, and retain- 

 ing traces of their original connection : ligament internal. 



1. Corneocyclas Hodgkini, Suter, 1905. Plate 54, figs. 8, a. 



Corneocyclas Hodgkini, Suter, T.N.Z.I., xxxvii, 1904 (1905), 246. f. 9 in 



text. 



Shell very small, oval, much compressed. Beaks obtuse, incon- 

 spicuous ; nepionic shell distinct, very finely concentrically striated, 

 passing without change into the adult valves. Anterior end produced 

 and attenuated, convex ; posterior and ventral margins regularly 

 rounded. Sculpture consisting of fine irregular concentric strise. 

 Colour yellowish-white. Usually with a thick ferruginous coating. 



Diameter Aut.-post., 2-75 mm. ; dorso-ventral, 1-75 mm. : thick- 

 ness, 0-75 mm. 



Type in my collection. 



Hab. Lake Waikaremoana, in 800 ft. (type) ; Lake Taupo, in 

 280 ft. and 320 ft, (Lucas and Hodgkin). 



