179 
The larg est and most beautiful species^ the scalaris, L.^ (to 
which Lamarck has since given a different name) was separated by 
Leach as the type of a new genus, to which he gave the name of 
Aciona ; it is the Wentletrap or royal staircase shelf^ of the 
English collectors, and Scalata of the French, belonging to the 
subdivision of this genus, which is distinguished by having the 
volutions separated, or only touching each other by the projecting 
ribs. This shell was very highly valued, and Leach mentions a 
specimen which was purchased at a sale for twenty pounds 3 but 
it is now (1815) estimated as worth double that sum.^^ Cubieres 
says that in his time, a fine specimen of four French inches long 
by three inches at base, was worth six thousand livres. To the 
same division of the genus, it is said, about twelve species are re- 
ferred. 
Blainville, after Plancus and Muller, describes the animal to be 
spiral, with a short oval foot inserted under the neck ; two tenta- 
cula, with filiform termination, supporting the eyes at the extremity 
of the inflated part ; a proboscis ? ; a long canal at the anterior right 
margin of the respiratory cavity ; sexes separate. 
They are all inhabitants of the sea. Lamarck has characterized 
seven recent and five fossil species ; but JDefrance enumerates 
twelve fossil species. 
SCALARIA CLATHRUS, Lin. — Turho clathrus, Linn. Gmel. &c. 
Scalaria communisj Lam. 
Scalaria clatJiruSj Auct. 
Desc. Variety c. Shell conic, turreted, imperforate, white, im- 
maculate : whorls from six to eleven, touching each other only by 
the ribs, but with a very narrow interval : ribs nine to each volu- 
tion, prominent, simple, a little oblique, somewhat recurved and 
with a more or less obvious, obtuse angle or shoulder above near 
the suture : aperture oval-orbicular ; base a little angulated : labium 
distinct. 
Length from three-fifths to nearly nine-tenths of an inch. 
Ohs. Inasmuch as the European specimens of dathrus in my 
collection are almost all colored, spotted .or banded and destitute 
of any obvious angle or shoulder on the ribs near the suture, and 
the suture is somewhat more contracted, I was led to describe 
this as a distinct species under the name of angulata ; but as the 
dathrus is often, and perhaps usually, destitute of color, and our 
