, 72 DISCOVERY REPORTS 



end. Anterior end a trifle more narrowly rounded than posterior end, both broadly and 

 evenly arcuate. Surface polished, showing very faint concentric growth lines but no 

 true sculpture. Hinge typical. Right valve with a large elongate-triangular cardinal at 

 the lower anterior part of the hinge plate, and a long narrow lamella above it, which is 

 hooked downward at its inner extremity ; behind the centrally placed resilifer there are 

 two long narrow diverging lamellae. Left valve with an anterior hooked cardinal and a 

 long medially thickened posterior lamella. Interior and valve margins smooth. 



Length 2-8 mm. ; height 2-3 mm. ; thickness (one valve) o-6 mm. (Holotype). 



Habitat: Off Three Kings Islands, St. 933, 260 m. 



This species differs from the genotype in being proportionately broader, less inflated, 

 and in having the outer surface smooth except for microscopic growth lines. In antipoda 

 there is a regular concentric sculpture of sharp closely spaced ridges. 



Notolepton subobliquum, n.sp. (Plate XLVII, fig. 6). 



Shell small, thin, semi-transparent, white. Subcircular, slightly inflated. Beaks small, 

 pointed, projecting. Anterior end somewhat narrowly rounded, descending sharply 

 from below the beak. Posterior end broadly rounded, dorsal part slightly higher than 

 the umbo. Medial section of the dorsal margin somewhat flattened. Sculptured with 

 closely spaced fine regular sharp concentric threads. Hinge typical. Interior and valve 

 margins smooth. 



Length 2-08 mm.; height 1-85 mm.; thickness (one valve) 0-51 mm. (Holotype). 



Habitat: Off Three Kings Islands, St. 933, 260 m. 



This species differs from the genotype in shape, having the umbos set more anteriorly, 

 and the posterior dorsal slope actually higher than the umbo. 



Genus Mysella, Angas 1877 

 Type (by monotypy) : Mysella anomala, Angas 



Mysella aupouria, n.sp. (Plate XLVII, fig. 5). 



Shell small, solid, white. Inequilateral ; anterior end about twice length of posterior 

 end. Beaks low and rounded, tips smooth and globular. Anterior end rounded, much 

 produced. Posterior end short and obliquely truncated below. Hinge typical; right 

 valve with two divergent cardinals, separated by the resilium. The cardinal anterior to 

 the resilium is the larger, being longer and more massive than the second cardinal, 

 which is posterior to the resilium. In the left valve thickened margins interlock with 

 grooves in the opposite valve, which are located between the cardinals and the margin. 

 These thickened margins of the left valve are rudimentary hinge teeth, for they are, 

 at their proximal ends, thickened into two small callosities, which interlock with the 

 cardinals of the other valve. Surface smooth except for regular weakly developed con- 

 centric growth lines. Muscle scars ovate subequal. Pallial line with a slight insinuation. 



Length 3-5 mm.; height 2-7 mm.; thickness (one valve) 0-9 mm. (Holotype). 



Habitat: Off Three Kings Islands, St. 933, 260 m. 



