HUCUUDJS. 117 



tus, vixque declivis; ventralis tantum convexus. Area concava, 

 carina definita ; labiis protrusis. Lunula nulla. Dentes utrinque 

 permulti. — Elongated oblong, twice as long as broad, without 

 anterior indented ray, but in its ordinary place marked towards 

 the lower margin with a few very obsolete radiating grooves. 

 General surface (polished, fide Kinds) traversed by shelving some- 

 what slantingly longitudinal sulci, which are fainter in front and 

 on the somewhat depressed umboes, and cease suddenly near the 

 posterior end, leaving a planulate narrow strip, which is crowded 

 with concentric wrinkles or striae. Hinder triangle smoothish or 

 finely wrinkled concentrically, and divided into three areas by a 

 carinated line, which bounds the escutcheon (which is concavely 

 impressed, but with pouting lips) by a very abrupt sinking of the 

 surface which angularly limits the lowest area in front, and by a 

 slightly raised radiating line, which stands halfway between these 

 two. Extremity of the slightly shorter anterior side attenuatedly 

 rounded ; posterior side not beaked, sinuously subtruncated, being 

 angulated by the triple projection of the radiations. Eront dorsal 

 slope decided, plano-convex ; hinder dorsal slope rather slight, 

 incurved. Ventral margin merely convex in front, straightish 

 and without indentation behind. No defined front dorsal area. 

 Teeth very, and nearly equally, numerous on either side of the 

 rather large, shelving, triangular cartilage-pit. Mr. Metcalfe 

 possesses two dead left valves. As the central keel does not 

 extend to the umboes, it is probably wholly absent in the fry. 



22. L. pella, Linnaus, f. 65, 66. — T. ovato-oblonga, ajquila- 

 teralis, postice superne abbreviato-cuneiformis, ventricosa, polita, 

 eburnea, striis arcuato-obliquis et antice divaricatis undique 

 sculpta. Regio postica superior angusta, subito excavata, angulo 

 inferne circumscripta, superne costii imbricato-squamosa. Margo 

 dorsalis utrinque subdeclivis, antice reetiusculus, postice subretusus, 

 demumque emarginatus. Area sulco profundo definita, trausversim 

 lirato-corrugata. Lunula iinpressa, lanceolata. — Ovate-oblong, 

 ventricose, glossy ivory-white, scarcely marked in front by an 

 extremely shallow broad indented ray, and behind by a very sud- 

 denly excavated acutangular curved triangle that is notched at 

 the base, is dorsally raised and squamosely imbricated, ventrally 

 simple and subcarinately angulated. Surface everywhere sculp- 

 tured by rather fine flexuously curved shelving stripe, which, for 

 the most part, run obliquely downwards with a double curve from 

 the front umbo, but before it arch in an opposite direction. Sides 

 equal : front extremity a little tapering, unsym metrically rounded : 

 hinder extremity briefly rostrated, its tip turned up and rounded 



