920 PELECYPODA. [Eulamfllibrcmckia. 



consisting of fine concentric growth-lines. Colour whitish. Interior 

 white, polished. Margins smooth, sharp. Hinge-line narrow, curved, 

 with a minute pseudo-tooth under the. beaks, a little more distinct 

 in the left valve. Ligament rather short, narrow, but very little of 

 it visible on the outside. Adductor-scars subequal, elongate. Pallial 

 line simple. 



Diameter Ant.-post.. 4-5 mm. ; dorso-ventral, 4-5 mm. : thick- 

 ness, 3 mm. 



Type in my collection. 



Hab. Off Otago Heads, dredged by Mr. A. Hamilton (type) ; 

 Milford Sound, in 100-120 fathoms, dredged by the scientific party 

 which visited the Sounds in December, 1908. 



Fam. LEPTONID^E, Gray. 



Animal marine, mantle without siphons and with 3 openings 

 an anterior branchial, a median pedal, and a posterior anal. Gills 

 with 2 gill-plates ; foot long and byssiferous. Hermaphrodite and 

 incubatory. 



Shell cellular-crystalline, with a periostracum ; valves equal, free, 

 smooth-edged, often gaping, variably sculptured ; adductor-scars 

 peripheral, subequal ; pallial line simple ; area obscure or none ; 

 ligament parivincular, opisthodetic, external, often obsolete ; resilium 

 usually internal, subumbonal or oblique ; hinge-plate narrow, chan- 

 nelled to receive the resilium ; hinge variable, normally consisting of 

 1 or 2 radiating cardinals and a pair of lateral laminae in each valve, 

 the anterior laminae often absent, and the posterior frequently closely 

 adjacent to the resilium. simulating cardinals. 



Cretaceous to Recent. 



SYNOPSIS OF GENERA. 



A. Hinge with 1-2 minute cardinals and 2 laterals in each valve, 



the latter sometimes double in the right valve. Resiliurn 



oblique, behind the beaks . . . . . . . . EEYCINA. 



B. Hinge with 2 cardinals, sometimes forming a A-shaped tooth, 



and 2 posterior laterals, the anterior laterals absent or 



feeble. Resilium large, under the beaks . . . . KELLIA. 



C. Right valve with an anterior triangular tooth and a hooked 



lamella above it, 2 posterior lamellae ; left valve with 1 



anterior hooked cardinal and 1 oblique posterior lamella. . NEOLEPTON. 



D. Shell inequilateral, anterior end longer. Right valve with 1 



pustular cardinal and 1 pair of laminae on each side ; left 

 valve with 1 cardinal and 2 lamina^ diverging from the 

 umbo . . . . . . 



E. Shell with prominent divaricate sculpture ; 1 cardinal in each 



valve, anterior and posterior laterals double in the right 



valve. Resilium in a sulcus below posterior lamella . . MYLLITA. 

 I 1 '. Each valve with a pair of lamella? on each side of the resilium . . PACHYKELLYA. 

 G. Right valve with 2 diverging cardinals, the resilium between 



them, and 2 laterals ; left valve with 2 simple laterals . . ROCHEFORTIA. 

 H. Right valve with 1 or 2, left valve with 2 or 3 cardinals ; no 



laterals ; ligament obsolete, resilium oblique . . . . CYAMIUM. 



