ornamented with thick concentric ridges, broader than the 

 intervening concave sulci, and rather distant thickish threads 

 which somewhat crenulate the margins of the lirse, but do not 

 pass over them ; inner margin of the valves strongly crenu- 

 lated on the ventral region, minutely so on the front dorsal 

 and posterior edges. Lunule small, shallow. 



Dimensions. — Antero-posterior diameter, 8*5 ; umbo-ventral 

 diameter, 8*25 ; sectional diameter, 7 millimetres. 



Locality. — Shell sand, Streaky Bay. 



This little species has a general resemblance to L. columhella, 

 Lamarck, but has its closest ally in L. nuciformis, Tate, a fossil 

 of the Older Tertiary beds of Aldinga Bay, from which it 

 differs by being less gibbous, less angulated behind, and by its 

 thicker lirse. 



Lepton ovatum, spec. nov. Plate v., fig. 11. 



Shell oval, thin, semitransparent, moderately convex, subin- 

 equilateral ; umbos, blunt, approximate, projecting beyond the 

 dorsal margin, slightly inclined to the front, situated a little 

 behind the centre. Margins rounded on sides, except dorsally. 



The sculpture consists of slight concentric stria? and 

 microscopic granules. Owing to the transparency of the 

 shell, the exterior exhibits the muscular scars and pallial line 

 of the interior. 



The right valve has one cardinal tooth, and the left valve two 

 cardinal teeth, each with a lateral on each side, those of the right 

 valve more remote. 



Dimensions. — Antero-posterior diameter, 2 ; umbo-ventral 

 diameter, 1'5 ; sectional diameter of closed valves, 1 milli- 

 metres. 



Locality. — Shell sand, Holdfast Bay. 



Kellia Angasiana, spec. nov. Plate v., fig. 7. 



Triangularly oval, inequilateral, rather convex, extremely 

 thin, dull, semitransparent. Dorsal margins sloping from the 

 beaks towards each end, somewhat roundly truncate on the 

 anterior side, roundly produced posteriorly, and the ventral 

 margin moderately curved ; umbo small, prominent, situated 

 considerably in front of the centre. 



The sculpture consists of numerous unequal elevated concen- 

 tric threads. 



Dimensions. — Antero-posterior diameter, 2 5 ; umbo-ventral 

 diameter, 2 ; sectional diameter of both valves, 2 millimetres. 



Locality. — Shell sand, Holdfast Bay. 



Montacuta meridionalis, spec. nov. Plate v., fig. 4. 

 Ovately orbicular, sub-equilateral, somewhat gibbous, ex- 

 tremely thin, glossy, transparent, margins rounded ; umbo 



