18 
PEO'FESSOE H. N. MOSELET. 
found in any of thè Chitonidse, measuring yy-yth of an inch in 
diameter. When seen under thè microscope, either by re- 
flected light or by transmitted light in thin ground sections of 
thè tegmentum, they are extremely brilliant and conspicuous. 
In Acanthopleura spiniger (see PI. VI, figs. 1, 2, 3, 
6) thè eyes are irregularly scattered around thè bases of thè 
tubercles with which thè surface of thè tegmentum is covered, 
and are confined, in thè specimens I bave examined, to thè 
region of thè margins of thè tegmenta adjoining thè girelle. 
The eyes of this species seem to be liable to be broken or to 
flake off in consequence of thè decay of thè surface laminse of 
thè tegmentum. Hence those remaining on old specimens are 
probably those most recently formed by thè mantle at thè 
margin of thè tegmentum. The process of thè formation of 
eyes pari passu with thè growth of thè shell has been already 
described. In some specimens apparently, according to thè 
existing systematic rules to be referred to thè species 
Acanthopleura spiniger, I bave been able to find no eyes 
at all. It will be necessary to examine a series of specimens of 
various ages to discover whether thè eyes are origiually more 
widely extended over thè shell surface in thè young or always 
marginai, and thus of late appearance in thè life of each in- 
dividuai in this species. 
In Acanthopleura s piniger there are large, prominent 
rounded tubercles on thè shell surface ; possibly they act as 
fenders to preserve thè eyes which He around their bases from 
attrition. The micropores and megalopores are borne on iso- 
lated, ovoid prominences of thè 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, marginai in positiou, but more numerous. 
In a large Corephium aculeatum, thè tegmenta of which 
were densely covered by a green alga, which pei’forates and 
penetrates thè shell substauce, immense numbers of eyes were 
