NUCULID^:. 61 



impressi obsolcti. Extreinitas postica latiuscula, obsolete biangu- 

 lata, vel ratundato-subrhomboidalis. Margo dorsalis anticus con- 

 vexus satisque declivis : posticus brcvis vixque declivis. Dentes 

 postici penmilti. — Suboval, rather compressed, much gaping at 

 both ends, white under a polished yellowish olive-coloured epi- 

 dermis, devoid of umbonal ridge or defined dorsal areas, merely 

 marked with concentric wrinkles of increase, with the indented 

 rays and their terminal retusions almost imperceptible. Anterior 

 side very decidedly the longer, tapering to a symmetrically rounded 

 extremity : posterior extremity broadish, either rotundately sub- 

 biaugulated or faintly rhomboidally rounded, the hinder end being 

 the more projecting. Front dorsal slope convex, moderately de- 

 cided ; hinder one very slight and short, excavated for the liga- 

 ment. Ventral margin convex, curving up moderately in front. 

 Teeth rather fine, numerous behind, scarcely any in front. — The 

 most striking peculiarity is, that the anterior side, which is the 

 shorter in Norrisii, is in this species the longer. 



3. S. ADSTRALis, Quo;/ and Gaim., f. 32. — T. subrhombea, 

 subiusequilateralis, ad umbones ventricosa, inferne compressiuscula, 

 cute fugaci vix nitida cinereo-lutescente induta, undique concen- 

 trice lirata : regio postica supera (ultra plicnm umbonalem con- 

 spicuam) tertiani superficiei implens, in medio retusa. Extremitas 

 lateris autici brevioris superne angulata, inferne oblique rotundata ; 

 postica superne angulata, in medio incurvata, inferne rotundata. 

 Margo dorsalis antice rectiusculus vixque declivis ; postice con- 

 caviusculus et acclivis ; ventralis in medio subretusus. — Sub- 

 rhombic, more or less ventricose at the umbonal region, plano- 

 convex below it, obliquely divided into two areas by an umbonal 

 ridge, which parts off a posterior triangle that occupies a full 

 third of the entire surface, and is retuse in the middle, gaping 

 considerably at the hinder extremity : dull-white under a rather 

 dull yellowish ash-coloured fugacious epidermis, everywhere (the 

 dorsal areas excepted) roughened by rather distant concentric 

 raised strije, otherwise unsculptured. Anterior side scarcely three- 

 sevenths of the entire length, angulated above by the almost ho- 

 rizontal straightish dorsal edge, obliquely rounded below. Pos- 

 terior dorsal edge concavely elevated, and so produced that the 

 angulated upper termination projects far beyond the rounded hinder 

 ventral extremity : posterior edge incurved in the middle. Ventral 

 margin subparallel to the dorsal, convex or subarcuated, except 

 in the centre, where it is somewhat retuse. Lips of the escutcheon, 

 which is sublinear and plano-concave, pouting. Lunulc very 

 narrow, if any. 



