PRESENCE OF EYES IN SHELLS OF CERTAIN CHITONID.®. 51 
rat us ; but the eyes in the shells of the Chitonidse may, by 
a little practice, be readily detected by examining the dried 
shells directly with a hand lens ; and I have examined rapidly 
in this way all the likely looking specimens in the extensive 
collection in the British Museum, and that at Montreal, and 
feel pretty certain that no eyes will be found in the genus 
Chiton, as now distinguished there. In Molpalia, Maugina, 
Lorica, and Ischnochiton, there are apparently no eyes as far 
as a cursory examination has yielded evidence to me. In 
Chitonellus there are certainly no eyes. 
The arrangement and the forms of the eyes vary conside- 
rably in different genera, and these characteristics will pro- 
bably prove of considerable value in the classification of the 
Chitonidae, which has hitherto proved so difficult a problem. 
The genus Scliizochiton is distinguished by having the 
mantle deeply notched posteriorly, in correspondence with a 
deep median notch in the hinder border of the posterior shell 
(PI. IY, fig. 1, c ). In Schizochiton incisus the eyes are 
restricted to single rows traversing the sutural lines. There 
are six rows of eyes on the anterior shell, corresponding with 
the number of marginal notches ; two on each of the middle 
shells, and six on the posterior shell — twenty-four rows alto- 
gether, with an average of about fifteen eyes in each, or in all 
360 eyes (see PI. IV, figs. 1, 2, 3, 4, 5). In the single specimen 
carefully examined all the rows except one have the eyes ar- 
ranged in a single straight row at regular intervals, but at the 
base of one row there are as an exception two eyes side by side. 
There are also in one or two places a very few irregularly scat- 
tered eyes on the arese laterales, showing that the condition 
here existing has probably been derived from an ancestral one in 
which the eyes were not concentrated into lines, but more widely 
diffused on the shell surface. In one row again, one eye is 
missing from the spot on which it ought to occur (PI. IV, fig. 
2). The rows of eyes are placed on raised ridges on the shell 
surface, formed by the development of tubercles on the promi- 
nent ridges with which the surfaces of the tegmenta are 
ornamented. The eyes in Schizochiton are the largest I have 
