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left valve,, and to find the two doubled teeth, so disposed and so grooved, 

 as exactly to receive the teeth of the opposite valve : he was also ena- 

 bled, by the same aid, to extend the number of species. Having, through 

 the kindness of Captain Gardiner, been favoured with many of the 

 Doctor's specimens, and having been also kindly assisted by Mr. Clarke 

 and the Rev. Mr. Cleeve, I am able to place before you nine species : 

 T. clavdlata, T. costata, T. eccentrica, T. aliformis, T. dadalea, T. spinosa, 

 E. sinuata, T. rugosa, and S. rudis. 



T. clavdlata curcirostra rugosa clave Hat a major *. Luid, A trigonal shell, 

 beset with nodular projections, disposed on the disk of the valves in rows, 

 in a transverse curved direction : on the anterior side, a sloping, slightly 

 rugose surface, widening from the beaks to the anterior point of the 

 valves, and ornamented with three crenulated ridges ; the innermost of 

 which enclose a long oval area, faintly marked with longitudinal striae, 

 and reaching from the beaks nearly to the anterior termination of the 

 shell. Beneath the beaks is a small sulcus, apparently for the reception 

 of the cartilage. Plate XII. Fig. 3. 



T. costata. A trigonal shell, with frequent rounded transverse ribs, 

 passing from the posterior margin to a crenulated ridge, which separates 

 the disk of the valves from the anterior or inferior sloping surface, on 

 which are, longitudinally disposed, three crenulated ridges, with six 

 smaller interposed ; the inner, of the larger crenulated ridges, enclosing 

 a flat long oval area, in the upper part of which is the depression for the 

 cartilage. Plate XII. Fig. 4. 



The preceding species have been long known on the Continent. The 

 person who first found them being a collector, contrived, by exchanging 

 them, to obtain a handsome collection of fossils. 



T. eccentrica. A transverse ovate-oblong shell, with transverse, obtuse, 

 rugose ribs, eccentrically disposed, and obliquely intersected by the lines 

 which mark the growth of the shell. Plate XII. Fig. 5. Specimens of 



* Curvirostra a Cardine (si in piano posueris) dextrorsum vel sinistrorsum reflexo, nomen 

 ohtinuit. 



