MARMAROSTOMA undulata. 
Waved Pearl Snail. 
rE EEE 
GENERIC CHARACTER. 
Shell turbinated, ponderous, the whorls generally angulated, the 
substance pearly: aperture circular, closed by a testaceous 
operculum: umbilicus none. 
Type, Turbo chrysostomus. L. 
Specific CHARACTER. 
Shell anguluied, variegated with green and brown undulated 
stripes, summit of each whorl coronated. 
ret Fe 
From the genera Turbo and Trochus of modern Concho- 
logists, we have detached ali those species whose shells 
are closed by a calcarious operculum; and this group we 
propose to distinguish by the name of Marmarostoma. 
The species, like ihe Trochi, properly so called, are all of 
a pearly structure; but their substance is much thicker ; 
the base of the shell is slightly produced; the exterior 
surface is marked either with tubercles, grooves, or ele- 
vated ridges ; and the aperture (from the convexity of the 
last whorl) forms a circle. If the student compares these 
characters with Trochus Zizyphinus, a common British 
shell, he will immediately perceive the leading differences 
between the two groups. 
But it is the calearious nature of the operculum (as in- 
dicating an important difference in the organization of the 
animal) which constitutes the primary character of Marma- 
rostoma: the particular structure of this appendage varies 
considerably in the different species: in some its outer 
surface is smooth and convex; and in others variously 
granulated. In the present shell it is marked by three or 
four deep semicircular grooves; that nearest the middle 
is the deepest, and terminates in an umbilicus. In some 
specimens, the spines on the principal ridge of the body 
whorl are nearly obsolete; but those which crown the sum- 
mit appear constant. 
We are indebted to the Rev. Mr. Bulwer, a scientific 
and arduous Conchologist, for our specimens of this new 
species, purchased by him in a collection sent from 
Panama. 
Marmarostoma PI. 1 
