NUCULID,E. 143 



circiter viginti. — Suboval, more or less ventricose, compressed 

 only at the hinder extremity, devoid of umbonal ridge, with a 

 polished cuticle of pale greenish-ash, or very pale yellowish-olive 

 colour, quite smooth. Anterior side occupying about three- 

 sevenths of the total length, unsymmetrically rounded. Posterior 

 side obverselv aud brieily subcuneiform, the tip well rounded and 

 dorsal : hinder edge plano-convex. Dorsal edges scarcely sloping, 

 the front one almost straight, the hinder one produced and in- 

 curved. Ventral margin subretuse in the middle, peculiarly and 

 convexly rising at both ends. Escutcheon very narrow and elon- 

 gated, barely refuse, carinately defined. Lunule indistinct, a 

 little depressed. Interior subiridescent. Cartilage-pit moderate, 

 spoon-shaped. Teeth about twenty on each side. 



60. L. Thraci.eformis, Storer, f. 4, 13. — T. ovalis vel obovalis, 

 postice subrhoinboidalis, ad umbones acutos ventricosa, subsequi- 

 lateralis, marginem versus concentricu corrugata, plica umbonali 

 rnunita, cute tenui vixque nitida induta. Margo dorsalis anticus 

 brevis, leviter declivis ; posticus incurvatus, haud declivis, cum 

 margine postico angulum obtuse formante. Extremitas postica 

 superne eminentior, interne oblique rotundata. Margo ventralis 

 auticus valde acclivis et oblique arcuatus. Area concava. — Oval 

 or oboval, subrhomboid posteriorly, ventricose at the umbonal 

 region, gradually declining in convexity beyond the gradually 

 developed umbonal ridge that parts off, in the adult, nearly three- 

 sevenths of the entire surface, much gaping at both extremities, 

 reddish-white under a rather dull fugacious epidermis, that ranges 

 in colour from olivaceous-ash to (more rarely) olivaceous-brown ; 

 coarsely and remotely wrinkled concentrically towards the outer 

 margin. Anterior side a little the shorter, unsymmetrically 

 rounded, its dorsal edge short, slightly convex, and a little 

 sloping. Hinder dorsal edge incurved, horizontal, forming a 

 blunt angle with the posterior edge, which is arched above but 

 more rectilinear and obliquely sloping inwards below, so that the 

 upper corner is far more prominent than the rounded lower extre- 

 mity. Ventral margin somewhat convex in the middle, obliquely 

 arcuated and much rising in front, with an occasional sinus before 

 the umbonal ridge. Lips of the escutcheon, which is concave and 

 linear-lanceolate, pouting. Cartilage-pit very large : pallial sinus 

 profound, and very large. Teeth not numerous (often fifteen to 

 seventeen). — The chief lateral projection is rather below the dorsal 

 line. The umboes are very prominent in young individuals, which 

 are quite smooth, are covered with a shining epidermis of a pale 

 greenish-ash colour, exhibit a more or less arched ventral margin, 



