78 ARCAD A. 
mixed up with a flake-white ovary; but from the extreme 
tenderness of the branchiz, I cannot speak of them and the 
palpi with certaimty as to form and number. 
July, 1852.—As I had just finished the above, a lively 
specimen of this species was met with, which, on being placed 
in water, at once unfurled its long and beautiful frmges, and 
exserted the ample niveous mantle and foot. This is certainly 
the Prince of British bivalves; the snow-white colour of both 
animal and shell sheds over this interesting creature the in- 
expressible charms of purity and elegance. It now lives in 
the same vase with its pigmy congener, the L. convexum. 
L. Ciarki# (nova species), Clark. 
L. Clarkie, Brit. Moll. iv. p. 255, pl. 132. f. 7. 
L. testa fragili, obliquo-subovali, compressa, postice et antice rotundata, 
albida, mediocriter nitida, striis concentricis, confertis, tenuibus 
notata; apices minutos, prominulos, subtilissime punctatos gerente. 
Latus rostris anterius, quoad longitudinem transversam, duplo 
posterius superat. In valva dextra, utroque, dentes laterales, 
duplices, distantes apparent; in sinistra, simplices ; inter quos, utra- 
que valva, dens unicus, primarius, erectus, acutus, oritur. 
Mensura obliqua ;/,, transversa ;/,, altitudo aut crassitudo ;1, uncie. 
Zonam corallinam Devonize meridionalis, prope ostium Iscze, rarius 
habitat. 
Animal ignotum. 
Of this minute and elegant species, a series of eighteen 
perfect specimens have occurred, and havmg compared the 
hinge and dentition with forty examples of the L. convexum 
and L. nitidum, I can state that there is not the slightest 
variation in this respect in the three species. Its distinguish- 
ing characters are the almost perfect obliquely oval shape, 
being without a trace of the subangularity which is Invariably 
seen at both extremities of the congeneric Leptons; and, as 
to the punctures, it is more devoid of them than the glabrous 
varieties of the L. nitidum, which, however, in the forty spe- 
cimens I possess, all show more or less the punctured aspect 
on the umbonal area; but mm the L. Clarkia only the apical 
circumscribed space is in some, but not in all examples, almost 
