150 UNIVALVES_— TURBO. 
class: the T. margaritaceus and T. argyrostomus are 
remarkable for the delicate coloring of their mouths. 
The T. delphinus may be adduced:as an example of 
the species of the fourth division. 
The fifth division contains some of the most beautiful 
species of the genus: they are in general thin and trans- 
parent, and strongly marked by rows of elevated conti- 
nuous ribs. The T. scalaris (the True Wentle-trap*), on 
account of its beauty and rarity, deserves a particular 
description. The shape of the shell (which is extreme-= 
ly elegant) is a spiral cone, formed by gibbous whorls, 
gradually decreasing from the base to the apex, un- 
connected by a columella; this circumstance, so com= 
pletely opposed to the regular structure of other turbi- 
nated shells, has occasioned considerable doubt as to 
its classification, and some authors have even placed it 
among the Serpule. The whorls are divided, at re- 
gular distances, by rows of elevated, suboblique, 
longitudinal ribs, which in young shells have a semi- 
pellucid appearance. The color is usually a yellow- 
ish or brownish white. The T. clathrus, or False Wentle- 
trap, is a very common shell, and much more taper 
and elongated than the T. scalaris. It has no umbilicus, 
and the whorls are closely united. 
The sixth division greatly resembles the preceding im 
form, and is only distinguished by its whorls not bemg 
surmounted with elevated cancellations. 
* Wentle-trap is derived from a German word, Windle-treppe, 
signifying a winding stair-case. 
