BIVALVIA. 127 
TELLIMYA BIDENTATA. Brown. Ilust. Brit. Conch., 2d ed, p. 107, pl. 44, figs. 8, 9. 
PETRICOLA — Gray. Aun. of Philos., 1825. 
— _— Hanley. Recent Shells, p. 54. 
ERYCINA ao Recluz. Rev. Zool., p. 331, 1844. 
— asa. Nyst. Coq. Foss. de Belg., p. 90, pl. 4, fig. 8, a—d, 1844. 
Mesopgesma ExicuuM. Lovén. Ind. Moll. Scand., p. 42, 1846. 
Spec. Char. Testé minutd, oblongo-ovatd, inequilaterali, levigata, tenui; postice ab- 
breviatd, obtusé angulatd, antice productd, rotundatd, vie attenuatd, margine ventrali 
et dorsali leviter arcuatis; dentibus duobus in utraque valvd; fovea ligamenti media 
subumbone demissa. 
Shell small, oblong or ovate, inequilateral, smooth, thin; posterior side short, 
obtusely angulated, anterior produced and rounded, scarcely contracted ; dorsal and 
ventral margins slightly curved; two teeth in each valve ; a moderate sized cavity for 
the ligament deeply situated beneath the umbo. 
Length, S;ths of an inch. Hezght, ds the length. 
Locality. Cor. Crag, Sutton and Gedgrave. 
Red Crag, Walton Naze. 
Recent, Britain, Scandinavia, and North America. 
Specimens of this species are by no means rare in the Coralline Crag, and I have 
found a few in the genuine Deposit of the Red Crag, at Walton Naze. Those from 
the latter or newer Formation correspond precisely with the recent shell from our own 
seas, and do not exceed it in size. The posterior side is considerably the shorter of the 
two, extending about one quarter the distance from the umbo that it does on the other 
side: the shell is smooth or very nearly so, and moderately tumid, the anterior or 
larger side forms half an ellipse, and the teeth are large and very distinct in the 
right valve, the one on the anterior side being the longer; those in the left valve 
are merely an angular elevation of the edge of the margin and inserted, when the 
valves are closed, into the depression between the teeth and margin of the right or 
opposite valve. The muscles are stated by M. Lovén to be large and powerful, but 
the impressions left by them in my specimens are very ill-defined, and by no means 
deeply seated. 
In the recent state as a British species it is not very abundant, and is said by 
British Conchologists to be generally found burrowing in very thick valves of dead 
Oysters. I have never seen the fossil in such a situation. 
2. Montacuta TruNCATA, S. Wood. Tab. XII, fig. 16, a, 6. 
Monracuta TRUNCATA. S. Wood. Catalogue, 1840. 
Spec. Char. Testa valde inequilaterali, cuneiformi vel subrhomboided, compressa, con- 
centricé striata; postice brevissimd, angulatd, antice productd, rotundatd, attenuata ; 
margine ventrali et dorsali rectiusculis ; dentibus duobus divergentibus, in valvd dextrd 
majoribus, foved ligamenti parva. 
