80 ARCAD At. 
equally important is, that the side anterior to the beaks is 
double the transverse length of the posterior one; whereas in 
all the other Leptons, of which I have more than a hundred 
examples, the beaks are nearly central, and they have more or 
less subangularity at the sides; therefore the oblique outline, 
rounded sides, and position of the beaks, are wnerring guides 
to distinguish the L. Clarkie from its congeners. 
The animal has not been cbserved. 
L. convexum, Alder. 
L. convexum, Brit. Moll. u. p. 102, and iv. p. 255, pl. 36. f. 10, mag- 
nified. 
L. nitidum, Turton et Auct. 
Kellia nitida, Brit. Moll. 11. p. 92, pl. 36. f. 3, 4. 
The animal inhabits a light greenish-yellow or pure white, 
subrhomboidal, moderately convex, more or less punctured 
shell. The mantle is frosted-white with the margins plain, 
but as much proportionately protruded beyond the edge of the 
shell as in L. sguamosum; it is m lke manner clothed with 
cirrhal filaments of about the same length, and of pruinose 
white, but unlike that species, they are rather less developed 
dorsally than ventrally ; each filament at its terminal edge is 
studded with four or five white pomts or cilia, so sharp and 
minute as to require a powerful lens to see them. There is no 
conspicuous leading process, as in the preceding species, but 
the mantle, at the same anterior pomt, forms a visible pro- 
jection or fold. In this species, and contrary to L. sguamosui, 
the longer and broader end is anterior, but the beaks are so 
central, that there is little difference in the sides; the single 
sessile anal tube is exactly as m the last species; there is no 
branchial siphon,— the water enters at the extensive ventral 
aperture. The foot is almost im every respect similar to that 
of its congener; it is perhaps larger in proportion, of pale 
azure hue, marked with intense but irregular flake-white 
minute bl tches; the posterior extremity is as long as the 
icr t» the pedicle; its termimation is perfectly 
portion ante ; 
y Y 
i + 
aciculate. and like its congener deevlv srooved 
aciculate, ana hke 1ts congener deeply grooved 
é JE 
e} 
I 
as far as the 
junetion with the body, at which pomt is the byssal gland, 
