492. TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
Siphono-pallial articulation—This is very weak in 
Hledone, as in all Octopoda. It consists of two shallow 
ridges on the postero-ventral edge of the funnel, which 
fit in two corresponding shallow grooves of the anterior 
and inner ventral surface of the mantle (Pl. II, fig. 9a, 
Gy eR UDATT AOE 
Vertical muscular septum.—This consists of two 
symmetrical triangular sheets of muscle, which run out 
from the mantle to the body and enclose the anus betsveen 
their anterior edges (Pl. II, fig. 8; Pl. III, fig. 11, m.s., 
m,s, and an.). The septum is covered by the general 
epithelium of the mantle cavity. The shortest side of 
each sheet is anterior, while the longest runs from the 
base of the mantle out obliquely to the visceral mass. 
The vertical line of attachment of the septum extends 
from the ventral posterior extremity of the mantle to 
within half an inch of its anterior edge (figs. 8 and 11, 4 
m.s.a.). By referring to fig. 11 it will be seen that after 
the septum enters the mantle cavity (e.m.), it 1s free for 
some distance from the visceral mass, and hence adheres 
only to the mantle. About half-way up the length of the 
oviduct, it becomes attached to the visceral mass. Hence 
there is free communication, posteriorly, between the 
right and left halves of the mantle cavity (fig 11, P.C.): 
Hach of the two halves of the septum consists of two 
rather thin sheets of muscle—(1) an upper sheet sloping 
from the mantle, obliquely inwards and downwards, to 
the body (figs. 8 and 11, m,); and (2)a lower sheet sloping 
from the mantle, obliquely inwards and upwards, to the 
body (figs. Sand 11, m.7.). 
The lower strands of the upper sheet and the outer 
strands of the lower sheet run towards one another, and 
form a superficial sheet which runs along with the funnel 
retractor muscle, down to the mantle (fig. 11, ml, 
