80 EOCENE MOLLUSCA. 
2. Arca avicuLina? Deshayes. Tab. XV, fig. 7, a, 6. 
ARCA AVICULINA. Desh. An. sans Vert. du Bass. de Par., t. i, p. 887, pl. 66, figs. 15—17, 
1858. 
Spec. Char. A. testa elongata, angusto-subcylindraced, depressiusculd, inequilaterali, 
radiatim eleganterque costellata ; costellis inequalibus, in medio tenuibus ; extremitatibus 
crescentibus, elevatis, subimbricatis ; umbonibus depressis, brevibus; ared connexiis parvda ; 
area dentali paucidentata. 
Shell slender, elongate, subcylindrical, somewhat depressed, inequilateral, elegantly 
covered with rays or small ribs; rays smaller or thinner in the centre, enlarging towards 
the lateral margins ; beaks small, depressed; area of the connector narrow; dental margin 
sparingly furnished. 
Length, \sinch; height, 2ths. 
Localities. Bracklesham, Bramshaw, Brook (Zdwards), Huntingbridge (Fisher). 
This is an elegant species, and, I believe, not very rare. There is considerable 
difference between our shell and the figure of the French species, to which it is here 
doubtfully referred ; but I feel unwilling to separate them upon what do not appear to be 
essential distinctions. There is also a difference between the British specimens from 
different localities, those from Bramshaw and Brook being more delicately rayed than 
those from Huntingbridge and Bracklesham. In general, our shell appears to be less 
cylindrical than that of the Paris Basin species; but in this character our own specimens 
vary materially. The principal difference is in the position of the umbo, which is more 
eccentric in the British than in the French shell, and in this character the former more 
closely approaches 4. interrupta, where the siphonal region is also broader or higher; but 
it differs from that species in being longer, differently rayed, and in having the central 
portion somewhat compressed, with an inflated or tumid siphonal region. * 
3. Arca BranGuLA, Lamarck. Tab. XIV, Fig. 1, a—/ 
ARCA BIANGULA. Lam. An. du Mus., t. vi, p. 219, 1809, and t .ix, pl. 19, fig. 4, a, 6, 1824. 
_— = Desh. Coq. Foss. des Env. de Par., t. i, p. 198, pl. 34, figs. 1—6, 1824. 
— Branperi. J. Sowerby. Min. Conch., t. 276, figs. 1, 2, 1821. 
— HyantuLta. Desh, Coq. Foss. des Env. de Par., t. i, p. 199, pl. 34, figs. 7, 8, 1824. 
= — Goldf. Petr. Germ., vol. i, p. 143, t. 122, fig. 3, a—d, 1826. 
Byssoarca Branperi. J. Sow., in Dixon’s Geol. Sussex, pp- 92, 169, t. 111, fig. 23, 1850. 

1 Since the above has been in press, I have seen the description and figure of Arca Laekeniana, Le 
Hon. (‘Deser. succ. de quelq. nouv. esp. des terr. tert. Hoc. des eny. de Brux.,’ p. 7, No. 15), a species which 
more resembles our fossil than does the one to which it is here doubtfully assigned, but the rays upon our 
shell are somewhat different; they are apparently more distant, and have intermediate strize, which are 
neither shown nor said to exist upon the Belgian fossil. I think, however, that when specimens of each 
can be compared, they may be found to be identical. 
