BIVALVIA. 
nr 
Or 
2. MytiLus HESPERIANUS, Lamarck. Tab. VIII, fig. 10. 
Myrtiius nesperranus. Lam. Hist. des An. Sans. Vert., t. vi, p. 127, 1819. 
Ss — Desh. 2d ed. Lam., t. vii, p. 48, 1836. 
= _ Payr. Cat. Moll. Cors., p. 68, pl. 2, fig. 5, 1826. 
— pEnsatus. SS. Wood. Catalogue, 1840. 
Spec. Char. Testé elongatd, obliqud, incurvaté densatd, crassd; margine dorsali 
arcuata. 
Shell elongate, oblique, incurved, thick and heavy ; dorsal margin convex. 
Greatest Diameter, 24 inches. 
Locality. Cor. Crag, Sudbourn. Recent, Mediterranean, and Coast of Spain. 
Two specimens only of this shell have yet come into my possession, and these are 
both of the right valve, and as they are all that I have seen, it does not appear to have 
been abundant during the Cor. Crag period. Fragments of a very thick Mussel, 
indicating a considerable curvature, and which I presume to belong to this species, 
are not unfrequently met with in various parts of the Red Crag; and as they have 
undergone a considerable deal of bouldering, may possibly have been washed out of 
the deposit of the antecedent period. I have given it therefore as a certain inhabitant 
of the older formation only. 
It appears to present characters different from any of the varieties of the common 
edible Mussel, sufficiently it is presumed to entitle it to be considered a distinct species. 
The variety called Myt. incurvatus, Mont., approaches nearest in form, but the dorsal 
margin is never so convex as in our shell, and the specimens I have seen are much 
thinner. The Crag shell is very thick, more especially in the narrow part near the 
beaks, and the anterior side curves inwardly, while the dorsal and posterior portions are 
particularly convex in outline ; the umbones are eroded, and the outer part of the shell 
near the beaks is so thin as to show the white lining through it, while towards the 
ventral portion the shell is of a deeper colour, as described by Payraudeau. My 
specimens are destitute of hinge-teeth, but their probable habitat in deep and more 
tranquil water may have rendered such unnecessary, and they may have thus become 
obsolete. 
Mopio0.La,* Lamarck, 1801. 
VousELLA. Scopoli, 1777, sec. Gray. 
CALLITRICHE et CALLITRICHODERMA. Poli., 1795. 
AmyGpatum. Megerle, 1811. 
CRENELLA. Brown, 1827. 
Bracuypontes. Swains., 1840. 
LanIstEs. Id. 1840. 
Moprorarca. Gray, 1840. 
Moprtotaria. Beck, sec. Loven, 1846. 
Lantstina. Gray, 1847. 
Moptotorsts? Mail, 1847. 
* Etym. Modiolus, 
