BIVALVIA. 127 



Tellimya bidentata. Brown. Ilust. Brit. Concb.., 2d ed, p. 107, pi. 44, figs. 8, 9. 

 Petricola — Gray. Ann. of Philos., 1825. 



— — Hanley. Recent Shells, p. 54. 



Erycina — Recluz. Rev. Zool., p. 331, 1844. 



— faba. Nyst. Coq. Foss. de Belg., p. 90, pi. 4, fig. 8, a — d, 1844. 

 Mesodesma exiguum. Loven. Ind. Moll. Scand., p. 42, 1846. 



Spec. Char. Testa minutd, oblongo-ovatd, incequilaterali, laevigata, tenui; postice ab- 

 breviatd, obtuse angulatd, antice productd, rotundatd, vix attenuatd, margine ventrali 

 et dor salt leviter arcuatis ; dentibus duobus in utraque valvd ; fovea ligamenti media 

 mbumbone 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, ^ths of an inch. Height, 4ds 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. Loven 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, b. 

 Montacuta truncata. S. Wood. Catalogue, 1840. 



Spec. Char. Testa valde inaquilaterali, cuneiformi vel subrhomboided, compressd, con- 

 centrice striata; postice brevissimd, angidatd, antice productd, rotundatd, attenuatd; 

 margine ventrali et dorsali rectiusculis ; dentibus duobus divergentibus, in valvd dewtrd 

 majoribus, fovea Ugamenti parvd. 



