PRESENCE OF ETES IN SHELLS OF CERTAIN CHTTONID^. 19 
found when thè alga was scrubbed off, and at thè most recently 
formed margins of tbe tegmenta not yet encroached upon by 
tbe plant (PI. VI, figs. 10, 11, 12). 
The eyes are very small and their cornese are ovai in outline, 
tbe long axes of thè ovalsbeing directed vertically in thè direction 
to tbe heights of tbe sbells. The eye-capsules reacb to only a 
small depth in thè thickness of thè tegmenta. The megalo- 
pores and micropores are disposed in vertical parallel lines with 
great regularity, thè megalopores occurring at regalar inter- 
vels in thè lines of micropores (PI. VI, fig. 11). A consider- 
ahle proportion of thè micrsesthetes are borne on strands inde- 
pendent of thè megalaesthetes. The tegmentary surface is 
covered with rows of tubercles, so disposed as to form regalar 
series radiating from thè apex of each shell, and also corre- 
sponding with one another in position horizontally. The eyes 
are never placed on thè tnbercles, bat lie on thè fiat snrface of 
thè tegmentnm between them, and it is possibly becaase of thè 
existence of thè tnbercles all over thè tegmentary snrface that 
thè eyes do not get entirely obliterated in thè older regions of 
thè shell. 
The eyes are present in enormous nnmbers. I estimate 
ronghly thè nnmbers present onthe anterior shell alone at 3000, 
connting only thè yonnger ones, which are in good condition, 
near thè free margins of thè tegmentnm, and not thè older 
more or less destroyed by thè boriug of thè shell by algae and 
animals on thè rest of thè arese. On thè remaining shells, at a 
moderate estimate, reckoning as before only thè eyes in toler- 
able condition, there mnst be at least 8500 eyes. 
InEnoplochiton niger thè eyes are excessively minate, 
and wonld not bave been recognised at all as sneh had not thè 
larger eyes in other forms been previonsly stndied. They are 
bere aìso confined to thè margins of thè tegmenta (PI. IV, 
figs. 6, 7, 8, 9). 
The cornea is slightly ovai, as in Corephinm aenleatnm, 
and as in that species thè megalopores and micropores are dis- 
posed in vertical lines. 
InTonicia marmorata thè eyes bave thè pecnliarity of 
3 
