Mr. W. Clark on a new British species of Lepton. 191 



XV. — On a new British species 0/ Lepton. 

 By William Clark, Esq. 



To the Editors of the Annals of Natural History. 



Gentlemen, Norfolk Crescent, Bath, Feb. 15, 1852. 



A NEW bivalve molluscum having occurred, I beg the favour of 

 you to insert its specific characters in the ' Annals,^ 



Genus Lepton, Turton. 

 L. Clarkia (nova species). 



L. testa fragili obliquo-subovali, compressa, postice et antice rotun- 

 data, albida, mediocriter nitida, striis concentricis, confertis, te- 

 nuibus notata ; apices minutes, prominulos, subtilissime pune- 

 tatos gerente. In valva dextra, utroque, dentes laterales, duplices, 

 distantes apparent ; sinistra, simplices ; inter quos, utraque valva, 

 dens unicus, primarius, erectus, acutus, oritur. Mensura obliqua y^j, 

 transversa y^Q, altitudo aut crassitude ^\y uncise. Zonam coral- 

 linam Devonise meridionalis, prepe ostium Iscse, rarius habitat. 

 Animal ignotum. 



Of this minute and elegant species, a series of eighteen perfect 

 specimens have occurred, and having compared the hinge and 

 dentition with forty examples of the L. convexum and L. nitidum, 

 1 can state that there is not the slightest variation in this respect 

 in the three species. Its distinguishing characters are the almost 

 perfect obliquely oval shape, being without a trace of the suban- 

 gularity which is invariably seen at both extremities of the con- 

 generic Leptons ; and, as to the punctures, it is more devoid of 

 them than the glabrous varieties of the L. nitidum, which how- 

 ever, in the forty specimens I possess, all show more or less the 

 punctured aspect on the umbonal area ; but in the L. Clarkice 

 only the apical circumscribed space is in some, but not in all 

 examples, almost invisibly punctured, which condition is rather 

 more pronounced within than on the outside of the apices. 



At one time I almost thought that the L. nitidum and L. con- 

 vexum might march together as a single species, subject to many 

 varieties ; but an increase of my series of both has, at least for 

 the present, made me doubt the propriety of considering the two 

 as identical. The animal of the L. convexum is still unknown, and 

 until it occurs, a safe determination on these points cannot be 

 made. The animal of the L. nitidum I know well, having in the 

 last summer observed two examples for four days ; it only differs 

 in some minor peculiarities from the L. squamosum^ one of which 

 I kept in sea-water thirty-four days, when it was killed whilst 

 still vigorous, in consequence of my departure from the sea-side. 



I may state, that in L. Clarkia the concentric striae of incre- 



