37 0 Proceedings of Royal Society of Edinburgh. 
[SESS. 
EXPLANATION OF FIGURES. 
Positions are given as viewed from above, except (as in the osphradium, fig. 
1, and the nephridial opening, fig. 5) where this does not indicate true morpho- 
logical position, for reasons explained in the text. The shaded part indicates 
the extent of the pallial cavity. The lettering in all the figures is the 
same, viz. : — 
an . , anal opening. 
au.f auricle. 
cer., cerata. 
ct., ctenidium. 
gen.j genital opening. 
gen.f., genital furrow. 
gl., gland. 
neph., nephridial opening. 
os., osphradium. 
pleur., pleuropodia. 
rhin., rhinophora. 
siph., siphon. 
tent., tentacles. 
ven., ventricle. 
Fig. 1. A siphonate Prosobranch. 
Fig. 2. Bulla. 
Fig. 3. Acera. 
Fig. 4. Doridium. 
Fig. 5. Aplysia. 
Fig. 6. Polycera. 
Fig. 7. Fiona. 
Fig. 8. Pleurobranchus. 
Fig. 9. Pleurobranchea, 
