1 ."is NUCULID^E. 



obliquis, posticis radiantibus, minntissiine sculpta. Margo dorsalis 

 utrinque vix declivis, antice brevis et convexiusculus, postice sub- 

 retusus ; ventralis in medio subretusus, demum rectiusculus et 

 oblique subangulatim acclivis. Lunula tenuiter striolata, per- 

 spicue definita, major quam area angustissima. — Oval-subrhombic, 

 small, subventricose at the umbonal region, gradually compressed 

 behind, ivory-white (sometimes of a yellow cast), glossy, smooth 

 to the eye, but under a powerful glass most minutely and closely 

 striolate ; the extreme front striolre nearly concentric, the next 

 sloping downwards and backwards, the hinder, which do not, 

 however, extend to the extreme verge, radiating, and, if possible, 

 still finer. Extremity of the anterior side, wdiich occupies about 

 two-fifths of the total length, and gapes considerably below, un- 

 symmetrically rounded. Posterior side neither beaked, nor much 

 attenuated, but with a rouuded-off angle above ; the hinder tri- 

 angle not defined by a distinct umbonal ridge, but well marked 

 near the umboes by the sudden decrease of the general convexity. 

 Front dorsal slope slight, short, plano-convex : hinder dorsal edge 

 scarcely sloping, at first subretuse, eventually plano-convex. Ven- 

 tral margin obliquely arching upwards in front, subretuse in the 

 middle, then convex and meeting the dorsal edge in an oblique 

 and straightish line. Escutcheon peculiarly narrow (obscurely 

 grooved?). Lunule larger, well defined, finely striolate length- 

 ways. — The epidermis is extremely thin, and somewhat iridescent. 



Sect. II., forming the Subgenus Yoldia. 



57. L. lanceolata, James Soicb., f. 12. — T. subovalis, antice 

 semielliptica, postice obtuse rostrata et paululum brevior, con- 

 vexa, oblique striata, cute nitida olivacea induta. Margo ven- 

 tralis antice arcuatus, postice convexus et raultum acclivis. Area 

 magna, abrupte impressa. — Suboval, not very strong, convex, 

 gaping at both ends, covered by a strong glossy (often dark) olive 

 cuticle, marked lengthways with moderately distant flexuously 

 slanting strife, which join some remote concentric stride, that run 

 from the front dorsal edge, along the obscure and very shallow- 

 anterior indented ray, and cease posteriorly at the broad smooth 

 site of an umbonal ridge. Front side slightly, yet decidedly, the 

 longer, semielliptical (the upper and lower slopes being almost 

 symmetrical) ; hinder side bluntly beaked, the almost subtruncated 

 tip (which in the adult shell is higher than the middle) broad, 

 slightly upturned, more prominent above. Hinder dorsal slope 

 moderate, at first convex, then incurved. Ventral margin arched 

 in front, merely convex but much rising behind, not refuse pos- 



