MANUAL OF THE MOLLUSCA. 
Distribution, 29 species. Cretaceous; India. Eocene. France. 
Netherlands. 
Eustoma, Piette, 1855. 
Type, H. tuberculosa, Piette. 
Shell in the young state resembling Cerithiwm ; in the adult 
the margins of the aperture are much expanded and posteriorly 
united by an indistinct canal; canal elongated. 
Fossil, 2 species. Great Oolite. Ardennes. 
EXELISSA, Piette, 1861. 
Etymology, xelisso, to unfold. 
Synonym, Kilvertia, Lycett, 1863. 
Type, Cerithium strangulatum, D’Archiac. 
Shell small, elongated, subcylindrical, somewhat pupzeform, 
many whorled, perpendicularly costated, tuberculated or spined ; 
last whorl cylindrical, contracted at the base, with a tendency 
to separate from the axis; aperture orbicular, entire, the lips 
elevated, produced, and slightly thickened; columella solid. 
Fossil, 14 species. Mid. Lias—Kimmeridge Clay. England 
and France. The shelly freestone of the Inferior Oolite, Glou- 
cestershire, contains some undescribed species. Cretaceous, 1 
sp. ? India. 
FIBULA, Piette, 1857. 
Example, Turritella Roissyi, D’Archiac. 
Shell elongated, columella straight, with a rudimentary 
groove near the base; outer lip arched, slightly notched at the 
suture; base of the aperture forming a slight canal, or rounded 
and entire, depending upon the exact period of growth at which 
the animal perished. 
The species of this genus possess characters intermediate and 
approximating them to Turritella and to Cerithiwm. 
Fossil, 21 species. Triassic—Cretaceous. Europe, India. 
CRYPTOPLOCUS, Pictet and Campiche, 1854. 
Etymology, cryptos, hidden; pploce, a plait. 
Example, Nerineea monilifera, D’Orb. 
Shell, as in Nerineea, without coiumella and labial plaits; one 
plait on the posterior face of the aperture, a disposition very 
analogous to that in some Cerithiwms, such as C. nodulosum, 
aperture rounded, not channeled in front; umbilicated or im 
perforate. 
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