( 64 ) 
ORDER V. PECTINIBRANCHI. 
4. Trocnoipa. 
Shell spiral, mouth en- 
tire, without notch or ca- 
nal. Pl. 9, fig. 7. 
2. Buccinoipa. 
Shell spiral, with a 
notch or canal for the 
passage of the siphon, 
which is a prolonged fold 
of the mantle. Pl. 10, fig. 
21. 
3. SIGARETOIDA. 
Shell flattened, hidden 
during life within a spon- 
gy buckler which is the 
true mantle. Pl. 5, fig. 25. 
PL. 14, fig, 15, 16. 
FAMILIES. 
An operculum. 
