Famiry PLEUROTOMIDE. 
Shell fusiform, with a more or less produced anterior canal, and 
a slit or sinus of the outer margin of the aperture near the suture. 
Operculum (not always present) corneous, annular, the nucleus 
apical, or subcentral and nearly marginal. 
Animal with widely separated tentacles, the eyes usually at or 
near their base ; mantle generally with a sinus on the right margin 
corresponding with the sinus of the shell; siphon long. Denti- 
tion: usually there are no central teeth, and the laterals are a 
single one on either side of the lingual band (1-0-1); but in 
some groups there is a central tooth, and in others there are 
two laterals. No jaws. 
The dentition, however it varies in minor respects, always pre- 
serves a resemblance to that of the Conide, Terebride and Can- 
cellariidz sufficient to include it with these in a great group 
Toxoglossa. The teeth are long, usually subulate, supplied with 
venom from a large gland (Pl. 33, fig. 52). 
There is some resemblance in the sinus of the shell between 
Conus and the principal groups of Pleurotomide ; and even in 
form, Genotia is connected, through Conorbis, with Conus. On 
the other hand Pusionella seems to form the connecting link 
with Terebra, Halia with Cancellaria, ete. 
In no other group of mollusks is it so difficult to make a satis- 
factory classification as in the Pleurotomide. The forms are 
exceedingly numerous, and known in many species to be very 
variable in their characters, whilst the material for the recognition 
of most of those described is generally scanty. Of the figured 
species, a very large proportion were described from single or 
few specimens,and most cabinets, however large, do not possess 
shells which can be certainly identified with these: then there is 
an unusually large proportion (amounting to hundreds) of un- 
figured species, the recognition of which is simply impossible. 
The many generic and subgeneric groups that have been made, 
far from enabling us to arrange the species in something like 
systematic order, only increase the confusion ; for so great is the 
variability of all the characters that nearly allied species have 
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