ORDER PECTINIBRANCHIATA. 57 
same plane; the aperture completely formed by the last whorl, 
and the margin not tumid: the animal similar to that of a 
turbo. 
The most common species, Turbo delphinus, Lin., List. 
608. 45, takes its name from the ramous and convoluted spines, 
which have caused it to be compared to a dried fish. Add 
Turbo nodulosus, Chemn., &c. 
PLEUROTOMA, Defrance. 
Fossil shells, with a round aperture, on the external margin 
of which is a narrow incision, ascending considerably. It is 
probable that it corresponded, like that of the siliquari, to 
some cleft in the branchial part of the mantle. 
M. Deshayes already enumerates upwards of twenty fossil 
species. The Sc_sSURELLE of M. dOrbigny are living 
species of the same. 
. 
TURRITELLA, Lam. 
The same round aperture as in turbo properly so called, and 
completed also by the penultimate whorl; but the shell is 
thin, and is so far from being convoluted in one plane, that its 
spire is prolonged into a turreted obelisk. ‘The eyes of the 
animal are placed on the:external base of its tentacula; the 
foot is small. (Turbo imbricatus, Martini, &c.) 
They are found in great numbers among fossils. ‘The 
Proto, Defr., should be approximated to them. 
ScALARIA, Lam. 
The spire, as in turritella, elongated into a point, and the 
aperture, as in delphinula, completely formed by the last 
whorl; it is, moreover, surrounded by a ridge, which the 
animal renews from space to space as its shell increases in 
size, so that it forms as it were steps. The tentacula and 
penis of the animal are long and slender. 
