89 ZOOLOGY. 
shell, where it forms a notch; and the apex of the shell is directed back- 
wards, whilst in Fissurella it turns forwards. 
Fam. 2. Calyptrwide. The shell of Calyptrea is patelliform or trochi- 
form, irregular, somewhat conical, with the apex rather posterior. Towards 
the apex of the inside there is a plate which is sometimes funnel-shaped, 
and sometimes like the vertical half of a funnel. In other species it forms 
a spiral, which approximates the sheil to that of the spirivalve genera. The 
animal is not spiral, the two tentacles are large and triangular, having the 
eyes upon an enlargement of the external side; the branchial cavity is 
large and oblique, and the branchie are pectinated, filamentous, and 
exsertile. Calyptrea sinensis (pl. 75, jig. 78). 
Crepidula has an ovate or piilones shell, generally convex above, the 
internal cavity divided some ‘Manes by a shelly diaphragm which 
represents the plate in Calyptrzea, and above which the viscera are placed. 
The animals of these two genera are alike, and the shells of some species 
present intermediate characters, so that it is difficult to tell to which of the 
two genera they should be referred. The Crepidule are sedentary, seating 
themselves upon stones, or upon each other, and adapting the margin of 
their shells to the irregularities of the object upon which they place 
themselves. 
Orver 9. Nematosprancuta (or Cirrhobranchia). The genus Dentaliwm 
( pl. 75, figs. 73-75) was for a long time believed to belong to the Annellida, 
until dissection proved it to be a molluse. The shell is a long, slender, and 
slightly curved cone, open at both ends, and sometimes ribbed or striate 
externally, as in D. elephantinum (fig. 73). The convex part of the shell 
corresponds to the back of the mollusc. The branchiz are composed of 
numerous extensible filaments forming a bundle upon each side of the neck, 
and it is probable that the branchize can be used to convey food to the 
mouth. The vent is at the posterior or smaller end of the shell, the lips are 
scolloped into a number of palpiform projections, and the ordinary tentacles 
and eyes are absent. The animal lives vertically in the sand with the head 
downwards. There are some shells which closely resemble those of 
Dentalium, and which were classed with them until it was ascertained that 
their animal is an annellid. They form the genus Ditrupa. 
Orper 10. Crenoprancuta (also named Pectinibranchia). This is an 
extensive order of dioicous spirivalve mollusca, in which the branchiz are 
pectinated, one or two in number, and placed in a large cavity above the 
neck; the tongue is armed with numerous teeth, the tentacles and eyes are 
usually two in number, and the aperture is usually closed by an operculum. 
Most of the families are marine, but some inhabit fresh water. The families 
are as follows: 1, Melaniide; 2, Cerithiide; 3, Vermetide ; 4, Trochide ; 
5, Pyramidellide ; 6, Buccinide ; 7, Purpuride ; 8, Strombide ; 9, Conidae ; 
10, Cypreidee ; 11, Volutidae; 12, Sigaretidee. 
Tah le oe Menke? 8 eee family named Turbmea is 
inapplicable, because in its various modifications it is used for the family to 
which Turbo belongs, by Lamarck and Deshayes, and by Blainville for a 
family of Polythalamia. Some of the genera of this family inhabit the sea, 
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