52 
PROFESSOR H. N. MOSELEY. 
found in any of the Chitonidse, measuring ,4~th of an inch in 
diameter. When seen under the microscope, either by re- 
flected light or by transmitted light in thin ground sections of 
the tegmentum, they are extremely brilliant and conspicuous. 
In Acanthopleura spiniger (see PI. VI, figs. 1, 2, 3, 
6) the eyes are irregularly scattered around the bases of the 
tubercles with which the surface of the tegmentum is covered, 
and are confined, in the specimens I have examined, to the 
region of the margins of the tegmenta adjoining the girdle. 
The eyes of this species seem to be liable to be broken or to 
flake off” in consequence of the decay of the surface laminae of 
the tegmentum. Hence those remaining on old specimens are 
probably those most recently formed by the mantle at the 
margin of the tegmentum. The process of the formation of 
eyes pari passu with the growth of the shell has been already 
described. In some specimens apparently, according to the 
existing systematic rules to be referred to the species 
Acanthopleura spiniger, I have been able to find no eyes 
at all. It will be necessai’y to examine a series of specimens of 
various ages to discover whether the eyes are originally more 
widely extended over the shell surface in the young or always 
marginal, and thus of late appearance in the life of each in- 
dividual in this species. 
In Acanthopleura spiniger there are large, prominent 
rounded tubercles on the shell surface ; possibly they act as 
fenders to preserve the eyes which lie around their bases from 
attrition. The micropores and megalopores are borne on iso- 
lated, ovoid prominences of the tegmentary surface ; each 
prominence bears a single megalopore on its summit, sur- 
rounded by a zone of micropores (PI. VI, fig. 3). 
In Acanthopleura piceus (PI. VI, figs. 8 and 9) there 
are somewhat similar tubercles to those occurring in A. spini- 
ger, but they show a tendency to form ridges. The eyes are, 
as in A. spiniger, marginal in position, but more numerous. 
In a large Corephium aculeatum, the tegmenta of which 
were densely covered by a green alga, which perforates and 
penetrates the shell substance, immense numbers of eyes were 
