224 Mr. E. L. Layard's Rambles in Ceylon. 



received into a corresponding cavity in the opposite valve ; there 

 is also occasionally in the right valve a small anterior, and in the 

 left a small posterior, accessory tooth upon the elevated margin 

 of the cavity; lateral teeth," one large posterior and approximate 

 in each valve, that of the left valve projecting, and i-eceived into 

 a depression formed oy the tooth or callosity of the other valve. 

 Muscular impressions oval ; pallial impression simple, faintly 

 marked. There is no lunule : the margin of the right valve an- 

 terior to the umbo forms a thickened projecting fold which covers 

 the tooth of the other valve, and is received into a corresponding 

 receding portion of the margin of that valve, so that the junctions 

 of the valves anterior to the umbones have a sinuous flexure. The 

 lateral teeth are remarkably large in our typical species ; they are 

 never altogether absent, but are much depressed in some other 

 species ; and when this variation occurs in connexion with a de- 

 pressed, oblique, and elongated cardinal tooth in the left valve, 

 the hinge is much altered in its aspect : the variation is exem- 

 plified by several species which occur in our Great Oolite and 

 in the Lias of the Meuse. 



The small accessory cardinal teeth are very uncertain in their 

 distinctness, and constitute only a minor and variable feature. 



The figure of Tancredia varies accoi'ding as the anterior or 

 posterior sides are the most produced ; several species have the 

 posterior side very short and convex, the figure then nearly 

 resembles that of the recent Donaces : all the species hitherto 

 discovered are destitute of ornament, they are remarkably smooth, 

 and exhibit but indistinctly the lines of growth. 



The number of species now known afford sufficient data for 

 comparison with other genera, and to determine its position in 

 the malacological system. To existing genera it would appear to 

 be only remotely connected ; but there are certain fossil forms, as 

 yet insufficiently known, which seem to approach to it in several 

 particulars ; but whether these latter forms, which are associated 

 with Tancredia in the same beds, are entitled to a position distinct 

 from existing genera, remains to be determined. M. Buvignier 

 has only indicated the position of Hettangia by placing it with 

 the Cardiacese. 



XXIII — Rambles in Ceylon. By Edgar Leopold La yard, Esq. 



To Richard Taylor, Esq. 



[Continued from vol. ix. p. 339.] 



My dear Sir, — I left off on the point of starting for our return to 

 the great central road, by a native path, through a line of country as 

 vet imopened by any government road, but which our energetic 



