TELLINA. 303 



bending to the left, their hinder to the right ; their surfaces 

 are very different, the left being almost smooth or merely 

 marked with concentric lines of increase, whilst the right is 

 diagonally striated with most delicate and crowded oblique 

 lines, which run from the upper part of the anterior side 

 towards the lower end of the hinder extremity. These 

 lines usually become converted into concentric striae adja- 

 cent to the front extremity, and do not cross the umbonal 

 fold (which is but little elevated) posteriorly. The ventral 

 margin is usually but little rounded, and is but slightly 

 inflected behind, where it is ordinarily straightish and but 

 little ascending. The sides are all but equal, the front is 

 well-rounded and but slightly tapering at its extremity, 

 whilst the hinder termination is attenuated below to an 

 obtuse point. The front dorsal edge, which slopes but 

 little, although straightish near the acute and rather pro- 

 jecting beaks, becomes more or less arcuated near the 

 extremity ; the hinder dorsal slope is very decided, and its 

 outline, which beneath the large and prominent ligament is 

 retuse, becomes convex near its termination. The posterior 

 tip is rounded. The front dorsal area is very slightly in- 

 flected. The hinge of the right valve is furnished with 

 an approximate front lateral lamina in addition to its 

 primary teeth. 



The ordinary size of this shell is about four-fifths of an 

 inch, and its breadth not quite half an inch at the widest 

 part. We have figured in plate XXVI. (f. S), an interest- 

 ing variety of this shell, observed by Mr. Jeftreys, in 

 which the oblique strise, gradually becoming indistinct an- 

 teriorly, wholly vanish near the front extremity. The 

 shape is likewise more abbreviated than in the typical 

 form, and the hinder termination is less attenuated than 

 usual. 



