(93 ) 
B. With bivalve shells, or none. 
4. ACEPHALA. 
No apparent head ; 
mouth hidden in the bot- 
tom or between the folds 
of a two-lobed mantle 
containing the branchiz 
and yiscera. 
5. BrAcutopopa. 
Mantle lobed; mouth 
exterior, between the ba- 
ses of two long fleshy 
arms supplying the place 
of a foot and with nume- 
rous filaments. 
6. CrkRHopPopA. 
With numerous hairy 
filaments, in pairs, com- 
posed of small articula- 
tions representing feet or 
fins, towards the orifice 
of the shell; mouth at the 
bottom of the shell. 
Branchiz composed 
of large leaves covered 
with vasculary  net- 
work, upon or between 
which the water passes. 
Branchiz composed 
of small leaves, ranged 
vound the edge of the 
inner face of each lobe. 
Hermaphrodite. 
Fixed, without the 
power of lecomotion. 
Ditto. 
