120 MR. W. E. HOYLE ON THE [Mar. 5, 
preserved: in one the cartilage was sacrificed to the dissection of the 
nervous system, and in the other it had already suffered a good deal 
of mutilation. I made a sketch of the fragments put together as 
carefully as possible, and afterwards compared this with the series of 
sections through the head of one of the smaller specimens. The two 
figures (Plate XIII. fig. 6) do not therefore represent a drawing of an 
actual specimen, but have been put together from these two sources. 
The basal portion of the cartilage, situated below and behind the 
united pedal and visceral ganglia, consists of an oblong box with a 
longitudinal septum down its middle. Each division is produced 
backwards as a blunt prominence; these are the receptacles in 
which the auditory organs are lodged. Anteriorly the sides of this 
box converge and the lower portion of the cartilage comes to consist 
of a vertical keel, which splits at its lower margin into two plates 
passing outwards and downwards below the eyeballs. These plates 
are each perforated near their outer margin by a foramen (osp.), which 
serves to transmit the nerve to the osphradium. At the point 
where the sloping subocular plate joins the vertical keel is a large 
foramen (v.f".), which serves for the passage of the veins from the 
eyes into the large vena cava. Another foramen in the middle line 
(v.f'.) gives passage to the veins from the central nervous system. 
From either side of the box a vertical plate is given off which lies 
upon the posterior surface of each eye. The vertical sides of the 
box are produced upwards and support a horseshoe-shaped plate, 
the concavity of which is directed backwards. The convexity extends 
much further forwards than the vertical supporting plates, and arches 
over a space in which the cerebral ganglia are situated ; its anterior 
extremity is bluntly pointed. There are no basi-brachial cartilages 
such as are seen in Sepia, but there is a thin plate of that material 
in the dorsal wall of the vena cava behind the cephalic cartilage and 
quite disconnected from it. 
The nuchal and siphono-articular cartilages (Plate XIII. fig. 7) 
present no special characters worthy of note. ‘The latter are of the 
linear kind common to the greater number of Decapoda; they 
exhibit a tendency toa slight curve, in the form of /. 
Of more interest is the presence of a pair of cartilages in the 
ventral wall of the siphon on its outer aspect. These are two thin 
plates (Plate XIII. fig. 7) of the form roughly of an isosceles obtuse- 
angled triangle, the median border being straight, the outer expanding 
to an angle. The sheet of cartilage is thickest near the middle line 
and thins out gradually towards the side, losing itself in the sur- 
rounding tissues. Their formation had not commenced in the 
smaller specimens: compare Plate XIII. fig. 5. 
The basi-pterygial cartilages had, however, developed to a con- 
siderable extent in these examples. The extremity of the pen lies 
in a groove between them. 
The pallial cartilages have a much more intimate connection with 
the structure of the body-wall than seems to me to have been 
hitherto recognized. ‘The nuchal cartilage commences as a thin 
plate which lies upon the muscles in the dorsal median line. Its 
