234 DESCRIPTIONS OF THE SFECIES OF LIMA. 



appears on the anterior side of some of those which belong to 

 the secondary formations, while those of more modern depo- 

 sits have the large opening for the byssus f on the posterior 

 side. I do not know whether I am right as to the universality 

 of this character, but it is uniform in all the species that I 

 have examined. Goldfuss has given figures of forty-six spe- 

 cies, (from the lias to the tertiary inclusive), and Deshayes 

 six more, from the Paris basin. 



1. Lima exilis, Nobis. Suppl. PI. No. 3, fig. 1. 



Shell inequilateral, oblique, slightly convex, slender, gaping, costated, (cos- 

 tee numerous, irregular, small, and distant), hinge-line oblique, ligamen- 

 tal area large, central pit rectangular, umbones distant, lunula smooth. — 

 Length, l£ inch, breadth l£ inch, depth one valve T 3 . 



Localities: Coralline crag, Ramsholt. 

 Red crag, Walton, Essex. 



The lines of growth are very distinct, and carried over the 

 ribs, producing a slight imbrication, giving the whole exte- 

 rior the characteristic roughness of the file : ribs sharp and 

 elevated on the anterior slope, but growing indistinct towards 

 the posterior side ; beyond the slope it is free from strife, the 

 opening for the byssus is on the posterior side near the hinge, 

 but it gapes also slightly on the other side near the front ; 

 the lines of the central pit diverge from the umbo at an angle 

 of 90°, pit projecting inwards, a slight depression is visible 

 internally, produced by the ribs, and it has one large, oval, 

 muscular impression near the posterior side. 



This is identical with a recent species in the possession of 

 Mr. G. B. Sowerby, without name or locality. 



2. Lima oblonga, Nobis. PI. 3. fig. 2. 



Shell oblong, inequilateral, oblique, depressed, gaping on both sides, cos- 

 tated, costee slightly waved, projecting beyond the edge, ligamental area 

 large, hinge-line oblique, umbones distant. Length 1 inch, breadth •&, 

 depth t|. 



Locality: Coralline crag, Ramsholt. 



Shell depressed, gaping on both sides, the anterior open- 

 ing large and somewhat triangular, with an internal margin, 

 striae numerous, becoming raised into costee as they approach 

 the anterior slope, beyond which it is smooth, lines of strice 

 slightly visible internally, and one large, lateral, sub -oval, 

 muscular impression. 



A recent species, Lima tenera, figured and described by 

 Turton in the ' Zool. Journal,' vol. ii. p. 363, tab. 13, /. 2, 

 much resembles this in general appearance, and may hereaf- 



