BIVALVIA. 125 



1. Leda amygdalojdes, /. Soioerby. Tab. XVII, fig. 6, a — c. 



Nucula amygualoides. J. Sow. Min. Conch., t. 554, fig. 4, 1821. 



— — Wetherell, Tr. Geol. Soc, 1834, p. 134. 



— — Morris. Catal. Brit. Foss., p. 217, 1854. 



Spec. Char. L. testa elongato-ovafd, crassd, titmidd, sub-aquilaterali ; concert- 

 trice striata, striis obtusis rot undis ; pedi-regione ovalo-rotundatd ; siphoni-regionc obtuse 

 rostratd ; area dentali crassiuscidd ; fossuld con nexus minutd, profunda. 



Shell elongately ovate, thick, tumid, glossy, nearly equilateral, and concentrically 

 striated; striae rounded; pedilateral margin ovately rounded ; siphonal region obtusely 

 pointed ; dental area rather thick ; cartilaginous depression small. 



Length, 1 inch ; height \ an inch. 



Localities. Highgate, Potter's Car, Wandsworth, Sheppey, tlampstead, Southend, 

 Whetstone Park, Finchley, Hornsey {Edwards and Wetherell), Cuffells {Prestwich). 



This is an elegant shell, and abundant in some localities, but seldom found with the 

 valves separated. Casts of this shell (at least what appear to be so) are found at Sheppey. 

 The nearest approach to this species is N. Deshayesiana, Nyst (' Coq. Poss. Belg.,' p. 221, 

 pi. xv, fig. 8) ; but that shell differs in being larger, thicker, with a more inflated and 

 more prominent umbo ; the stria) in the British shell extend to the extreme margins, and 

 cover the entire surface, as they do also in N. Deshayesiana. There is a distinctly marked 

 corselet as well as lunule on each side of the umbo, with an elevated ridge ; this is not so 

 distinctly marked in the Belgian shell, and the siphonal region of this latter species is 

 rather the more pointed of the two. There are about fifteen or sixteen denticles on each 

 side of the hinge-area of our shell, and the sinus in the mantle-mark is very shallow. 



2. Leda costulata, Deshayes. Tab. XVIII, fig. 3, a, b. 



Leda costulata. Desk. An. sans Vert, du Bass, de Par., t. i, p. 829, pi. 6f>, figs. 8 — 10, 



1858. 



Spec. Char. L. " testa ovato-transversd. subtrigond, soliduld, depressiusculd, eequildterali, 



antice obtusd, postice vix rostratd, transversim regulariter sulcata ; umbonibus mini mis. 



conniventibus ; lunula laevigata, vix dislincld ; ano clongato, lanceolato, convexiusculo, angulo 



obluso separaio ; margine cardinali angusto ; dentibus serialibus minutissinris, appro rimatis ; 



fossuld ligamenti minulissimd.''' — Dcsh. 



Shell elongate, ovately subtrigonular, strong, somewmat depressed, equilateral ; pedilateral 

 margin ovately rounded; siphonal region scarcely rostrated, covered concentrically with broad 

 ridges and furrows ; beaks small; lunule indistinct ; corselet elongate, slightly convex, e\- 



