nucuud/f;. 15 



liinder side quickly forming an upturned beak, of which the rather 

 narrow tip is convex, and above the middle. Front dorsal slope 

 slight, straightish ; hinder dorsal slope moderate, deeply incurved. 

 Ventral margin much arcuated, rising obliquely in front, not re- 

 tuse behind. Escutcheon large, detined, finely grooved length- 

 ways. Lunule inconspicuous. Teeth numerous on both sides. 

 Judging from the nucleu.s, the fry may readily be mistaken for a 

 distinct species. Montagu described the species as new, and not 

 as of Gmeliu, whose rostrata was identical with perniila. 



25. L. Chova, Grai/, f. 67. — T. L. eras-see similliraa, brevior 

 autem, ovato-acuta, margine dorsali utrinque decliviore, ventrali 

 magis arcuato ; rosfri extremitate altiore, magisque acuminata. 

 Lyra; plica' umbonalis nonuunquaiu inferne snbobsoletse. — Most 

 closely resembling crasxa, but is peaked-ovate ; the slopes are con- 

 sequently more decided, and the ventral margin more arched; the 

 peak is rather more acummated, and higher seated; the lyrae, too, 

 are scarcely so prominent, and the arched ones on the umbonal 

 ridge become, occasionally, almost obsolete at the lower extremity. 

 The difference between this and crassa, var. brevior, is very 

 trilling. 



20. L. coM'USA, Hanley, f. 85. — T. Ecquilateralis, ovali-acuta, 

 postice rostrata, baud ventricosa, cute cinerea induta, sulcis densis 

 concentricis undique sculpta. Rostri extremitas recurvata, acute 

 angularis. Plica umbonalis neque alta, nee antice detinita. Margo 

 ventralis antice convexus, vixque declivis ; postice declivis, principio 

 rectiusculus, demum repente incurvatus; ventralis utrinque acclivis, 

 antice arcuatus, postice baud sinuatus. Arete dorsales magnte, 

 lanceolatip, labiis protusis : area sublongitudinaliter sulcata : lu- 

 nula impressa. — Peaked-oval, convex or subveutricose, with a 

 shining ash-coloured epidermis, closely, regularly, and concentri- 

 cally grooved throughout (the dorsal areas excepted) ; sulci shelv- 

 ing in front, their intervals converted into flattened costse on the 

 umboes and towards the umbonal ridge, which latter is neither 

 elevated nor defined in front. Sides equal, or very nearly so : 

 anterior extremity rounded ; posterior side rather abruptly beaked, 

 the ti[), which is either in the middle or just above it, upturned 

 and sharply angular. Front dor-^al slope very slight, convex, with 

 a sudden terminal retusion. Hinder dorsal slope moderate, at 

 first straightish or plano-convex, eventually rather suddenly in- 

 curved. Ventral margin much rising at both ends, arcuated (at 

 the least, in front), devoid of retusion. Dorsal areas large, pouting, 

 lanceolate; escutcheon carinately defined, sublongitudinally grooved; 



