166 THE GASTROPODA 
pore. Faminty 15. Harpipar, Chenu. Foot very great ; without oper- 
culum; shell with a short spire and longitudinal ribs; siphon long. 
Genus—Harpa, Lamarck. 
TRIBE 2, TOXIGLOSSA. 
Stenoglossa without jaws, and with a radular formula of 1.0.1; a 
““poison gland” present, whose duct traverses the nerve-collar. 
Faminy 1. PLEUROTOMATIDAE, Loven. Shell fusiform with an elongated 
spire ; the margin of the shell and mantle notched ; siphon rather long ; 
eyes situated on the sides of the tentacles. Genera—Clavatula, Lamarck ; 
operculum piriform with a lateral nucleus ; eyes near the extremities of 
the tentacles. Pleurotoma, Lamarck ; operculum oval with nucleus near 
the summit ; eyes near the bases of the tentacles. Mangilia, Risso ; no 
operculum ; eyes half-way up the tentacles. Bela, Gray. Pusionella, 
Gray. Pontiothawma, Smith. Faminy 2. TrrEBRIDAE, Adams. Shell 
turriculated, with numerous whorls ; aperture and operculum oval ; foot 
small ; eyes at the summits of the tentacles; siphon long. Genus 
Terebra, Adanson. Famity 3. Contpar, Gray. Shell conical, with a 
very short spire and a narrow aperture with parallel borders; eyes 
borne near the middle of the external sides of the tentacles ; an ungui- 
form operculum. Genus—Conus, Linnaeus (Fig. 144). 
Sus-Ciass II. EUTHYNEURA, Spengel 
(= Platymalakia, von Jhering = Androgyna, Mérch). 
These are hermaphrodite Gastropoda, whose radula is generally 
composed of uniform teeth on each side of the median tooth 
(Fig. 145). The head in most cases bears two pairs of tentacles ; 
it is only in Lophocercus, 
the Elysiomorpha, 
Hedyle —milaschewitchi, 
and the Janellidae that 
there is a single pair. 
The Euthyneura are 
De specially characterised 
ale. (rom Lankester, ater Loven.) «Dy bhedetorsiomof them 
organisation whenadult; 
this detorsion is particularly well manifested in the visceral com- 
missure, which is no longer twisted, except in some archaic forms 
of Tectibranchs (Actaeon, Fig. 57) and Pulmonates (Chilina), and 
shows a tendency to the concentration of all its elements round 
the oesophagus (Fig. 146). To such a degree is this concentration 
carried that, with the exception of the majority of the Bullomorpha 
and of Aplysia (Fig. 95), the whole central nervous system is 
aggregated in the cephalic region (Fig. 97), sometimes on the dorsal 
side, as in the Pleurobranchidae and Nudibranchia (Fig. 159), 
sometimes on the ventral side as in the Thecosomata (Fig. 60, 7.s). 
The pedal centres are frequently united by a second “ parapedal ” 
