BIVALVIA. 169 



able variation. M. Deshayes says ('An. sans Vert, du Bass, de Par.,' p. 741), "La 

 sinuosite du bord ventral, d'apres laquelle nous avons choisi le nom specifique, ne se pre- 

 sente que dans le plus petit nombre des individus." I have, therefore, upon that report, 

 permitted the British fossil to stand doubtfully with the above name. Our shell does 

 not exhibit a marginal sinuosity, but in other respects it seems to correspond. 



10. Crassatella Sowerbyi, Edivards MS. PI. XXIII, fig. 6 a, b. 



Crassatella compressa, J. Sowerhy (non Lam.). In Dixon's Geol. of Sussex, p. 88, 



pi. ii, fig. 2, 1850. 



Sjjec. Char. Cr. Testa transversa, irrer/ulariter trianpdari, crassd, compressiusculd, 

 inaquilaterali, suhlamgatd, aut ad imihonem sulcis paucis distantihus ; pedi-regio7ie ad mar - 

 ginem convexd, altera majiore productd, angulatd et truncatd ; umbonibus depressis ; lunula 

 elongato-lanceolatd ; cardine incrassato, unidentato in valvd dextrd, in altera bidentato ; 

 marginibus in medio crenulatis. 



Shell transverse, irregularly triangular, thick, rather compressed, inequilateral, sul- 

 cated in the umbonal region, smooth on the outer or older part of the shell ; pedal margin 

 rounded ; siphonal side angulated and truncated ; beaks rather depressed and obtuse ; 

 lunule elongate, not very deep ; hinge thick, one tooth in right valve, and two in the 

 left ; ventral margins crenulated in the middle. 



Length, l^th inch ; height, f ths of an inch. 



Localities. Bracklesham, Stubbington, White Cliff Bay [Edwards). 



Mr. Edwards has separated this from compressa of Lamarck, in which I agree with 

 him. It somewhat resembles the variety called hemileia, but it is distinguished by 

 being constantly more free from ridges and more compressed. Fig. 13 of the same Plate 

 represents a specimen which has had the MS. name of Hantoniensis affixed to it by Mr. 

 Edwards. In PI. XXIV I have also had represented two other forms, to which have 

 been affixed the respective names of C. semi-lcevis (fig. 15) and C. obesa (fig. 16 «, b). 

 The first of these two is from Bracklesham ; it varies in shape in being more elongated, 

 and it has finer ridges over the umbonal region. The other is from Stubbington ; it is 

 shorter and more tumid. These have all been considered by Mr. Edwards as specifically 

 distinct, and possibly they may be so, but for the present I regard them as varieties. 



11. Crassatella subquadrata, Edwards. PI. XXIII, fig. 12. 



Spec. Char. Cr. Testa transversa, subquadrangulatd, tum,idd, Iceviuscidd, incequilaterali ; 

 pedi-regione minor e ; altera truncatd vel subquadrata ; umbonibus obtusis, elevatis ; siphoni- 



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