NUCUT.IB.E. 1 1 •'! 



liris concentricis (quanim interstiiia ferme sunt latinvii) undique, 

 etiam in plicam umbonalem concentrice et regulariter rugosa. — 

 Resembling pernida, but smaller, oil-yellow, peculiarly compressed 

 when young, almost or wholly devoid of an indented ray, concen- 

 trically traversed by even and regular lyrated stria? (whose inter- 

 vals are, if anything, rather broader), which are equally perceptible 

 on both valves and pervade alike the umbonal ridge : front ex- 

 tremity more symmetrically rounded. 



14. L. pernula, Midler, f. 56-58.- — T. suboblongo-rostrata, 

 valde inaequilateralis, convexa, cute olivacca vel olivaceo-lutescente 

 induta, rugis elevatis tenuibus, in medio densis, ante radium im- 

 pressum anticum remotioribus minusque argutis, ad extremitatem 

 posticam subobsoletis, concentrice striata. Margo ventralis antiee" 

 oblique arcuatus et multum acclivis ; postice rectior, demumque 

 subretusus. Area acute definita, multum producta, labiis pro- 

 trusis ; lunula obsoleta. — Jar. Margin) bus dorsalibus magis de- 

 clivibus ; postico incurvato. — Peaked elongated oblong, com- 

 pressed behind, from convex to subventricose in the middle, with 

 a more or less manifest indentation radiating with little obliquity 

 from the beaks to nearly the front extremity of the opposite 

 margin, clothed with a glossy epidermis that ranges in tint from 

 yellowish-olive in the adult to olivaceous-yellow in the young, 

 very closely and finely sculptured by raised concentric wrinkles, 

 which, coarser and more distant before the indentation, become, 

 for the most part, wholly or partially obsolete towards and upon 

 the umbonal ridge (except, perhaps, above) and lunule, and are 

 usually less conspicuous on the left valve. Posterior side about 

 twice as long as the anterior (which is unsymmetrically rounded), 

 subrostrated, and very gradually tapering to a very narrow trun- 

 cated subcentral tip ; umbonal ridge rather broad and flattened, 

 not much raised, often divided by an indistinct groove. Front 

 dorsal edge subrctuse, moderately sloping ; hinder dorsal edge 

 higher, convex, less sloping. Ventral margin much and obliquely 

 rising in front, arched anteriorly ; posteriorly rather straighter, 

 moderately rising, with a slight refusion before the ridge. Lips 

 of the escutcheon, which is very long, and sharply defined, pout- 

 ing. Lunule obsolete. Teeth on the average sixteen and twenty- 

 four. — Far. Both slopes more decided ; the hinder one incurved. 



15. L. buccata, Steensfrup, f. 6.'3, 64. — T. sp. prjecedenti si- 

 millima, sed brevior, minus ineequilateralis, magis ventricosa, mar- 

 ginibus dorsalibus magis declivibus, area latiore. — Most closely 

 resembling an abbreviated pernula (being less elongated), but 



VOL. III. N 



