42 TRACHELIPODA. CERITHIUM. 
part of the front of the body ; columella plaited, varying in 
number and size; for the most part, they are large, com- 
pressed, and much developed; in some instances they are 
small, few, and placed far within the columella, so as to be 
nearly obscured; at other times low down. 
Cancellaria evulsa. Plate IV. fig. 35. Found in the 
London Clay at Barton Cliff. 
Sowerby proposes that this genus should be separated into the following 
sections ;— 
1. The canal short, recurved, and produced; the superior fold on the 
columella compressed. 
2. The canal short, recurved, and produced ; the columella with two plaits, 
the lower one largest ; the varices few, and irregular. 
3. Aperture terminating in a produced canal; columella three-plaited ; 
with distinct cleft varices. 
4. Aperture terminating in a produced canal; columella two-plaited, and 
inflected towards the outer lip, 
The genus consists of but few species, which are natives of the coasts of 
America, Africa, and the Indian Seas. 
Fossil species are not uncommon, and occur in the London Clay at Hord- 
well, and in the same formation at Piacenza; the Calcaire-grossier of Bordeaux, 
Cotentin, and Paris. 
_ Bruguiére placed several species of this genus among his Mitre, as also 
some of the Marginellz, Ancille, and Colombelle; some of the Cancellarie 
approach near to some species of the genus Turbinella, but the transverse 
grooves on the outer lip is a strong distinguishing feature in the Cancellaria. 
Genus XXX VI.— PLEUROTOMA. — Lamarck. 
Generic Character. — Shell fusiform, thick, turreted ; 
spire generally longer than the body ; aperture oval, with 
a canal more or less elongated at the base; outer lip thin, 
with a notch or fissure at the upper part, contiguous to the 
suture ; columella smooth and nearly straight ; operculum 
horny, acuminated; its nucleus situate at the lower ex- 
tremity. Some of the species are covered with a thin epi- 
dermis. 
Pleurotoma priscus. Plate 1V. fig. 4. Found in the 
London Clay at Hordwell. 
The Pleurotome are Oceanic shells, inhabiting the seas of Southern Europe, 
and the warmer portions of the globe. 
Fossil species are only met with in the Tertiary formations, namely, the 
London Clay, Calcaire-grossiér, with other contemporary strata of Bor- 
deaux, and the Arpenines. 
Genus XXXVII.— CERITHIUM. — Bruquiere. 
Generic Character, — Shell greatly lengthened, or tur- 
reted ; with numerous volutions, more or less tubercular, 
or spinous, or rough, in a very few instances smooth, or 
