BIVALVIA. 169 
able variation. M. Deshayes says (‘An. sans Vert. du Bass. de Par.,’ p. 741), “La 
sinuosité 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 Sowersyl, Ldwards MS. Pl. XXIII, fig. 6 a, 4. 
CRASSATELLA COMPRESSA, J. Sowerby (non Lam.). In Dixon’s Geol. of Sussex, p. 88, 
pl. ii, fig. 2, 1850. 
Spec. Char. Or. Testd transversd, irregulariter triangulari, crassa, compressiusculd, 
inequilaterali, sublevigatd, aut ad umbonem sulcis paueis distantibus ; pedi-regione ad mar- 
ginem convexd, alterd majiore producta, angulatd et truncatd ; umbonibus depressis ; lunuld 
elongato-lanceolata ; cardine incrassato, unidentato in valvd dextrd, in alterd 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 nght valve, and two in the 
left ; ventral margins crenulated in the middle. 
Length, 13th inch; height, $ths of an inch. 
Localities. Bracklesham, Stubbington, White Cliff Bay (2dwards). 
Mr. Edwards has separated this from compressa of Lamarck, in which I agree with 
him. It somewhat resembles the variety called emileca, 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 Hantomiensis affixed to it by Mr. 
Edwards. In Pl. XXIV I have also had represented two other forms, to which have 
been affixed the respective names of C. semi-levis (fig. 15) and C. obesa (fig. 16 a, 4). 
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. ‘he 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. CrassaTeLta supquaprata, Hdwards. Pl. XXIII, fig. 12. 
Spec. Char. Cr. Testa transversd, subquadrangulata, tumidd, leviusculd, inequilaterali ; 
pedi-regione minore ; alterd truncata vel subquadratda ; umbonibus obtusis, elevatis ; siphoni- 
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