42 
PROFESSOR H. N. MOSELEY. 
offsets enter the canal plexus by two sets of openings ; firstly, 
at the margins of the tegmenta, which adjoin the borders of the 
girdle by a series of fine apertures in the shell substance, 
which occupy narrow band-like areas intervening between the 
tegmenta and upper surfaces of the articulamenta at their lines 
of junction with one another. These bands are sieve-like in 
appearance, being perforated all over, and lie just beneath the 
external margin of the tegmenta. Secondly, offsets of the 
mantle tissue enter the canal plexus at the incisurae, and by 
means of fine pore-like apertures on the under surfaces of the 
shells. These pores may be irregularly scattered, as, e. g. in 
the case of the anterior and posterior shells of Corephium 
aculeatum, or they may be concentrated along the so-called 
sutural lines of the shells which spring from the marginal 
notches or incisurae. The sutural lines where present in the 
anterior and posterior shells radiate from the apices (or 
mucrones) of the shells to the marginal notches. There are 
six such radiating sutural lines in the anterior shell of Schi- 
zochiton, and six corresponding notches (see PI. IY, fig. 5.) 
On each median shell there are a single pair of lateral sutural 
lines, and a corresponding single pair of notches. The sutural 
lines are marked on the under surfaces of the shells by a series 
of small slit-like apertures, directed transversely to the lengths 
of the lines, and when the shell is removed from its bed corre- 
sponding minute transverse processes of the mantle are seen 
projecting along corresponding lines on its surface, and torn 
across. Processes of the mantle tissues also enter the shell 
canals at the bottom of each marginal notch, and from the 
notch longitudinal canals run in the shell substance along the 
sutural lines above the series of slit-like apertures. 
The strings of soft tissue forming the horizontal plexus show 
a finely fibrous structure, and contain numerous nuclei and 
fine granular matter. They are not canals as believed by 
Marshall. They contain nerve-fibres within them, as is 
certain from the fact that some of them expand into retinas of 
typical structure in the eyes. I have been unable to trace the 
nerves supplying the soft tissue ramifications of the tegmenta 
