HYALONEMA (HYALONEMA) AGASSIZI. 
173 
preserved. Its body is broad top- or spindle-shaped, has at every level a nearly 
circular transverse section, and measures 66 mm. in length and 48 mm. in maxi- 
mum transverse diameter. At its apex the rounded summit of the nearly cylin- 
drical gastral cone is visible. The cone is surrounded by a circular wall which 
terminates in a narrow frill, the margin of which appears as a circle 8 mm. in 
diameter. The circular wall is separated from the cone by a circular fissure 
about 1 mm. wide. This fissure is the gastral cavity. The outer surface of the 
sponge-body is quite smooth and continuous; apertures, visible to the naked eye, 
do not occur in it. From the lower, rounded end of the body the stalk arises. 
At its origin this is about 5 mm. thick, thickens slightly below, and measures a 
little over 40 cm. in length. The spicules composing it are all broken off at the 
lower end; in life the stalk was probably considerably longer. Its lower and 
central parts are quite straight. Its upper part is strongly and uniformly bent- 
through an angle of about 60°. 
The single specimen of form B (Plate 41, fig. 1) is not so well-preserved. 
Of its dermal membrane only a few patches are left and the upper part is much 
torn. It is massive, pear- or club-shaped, 81 mm. long and 61 mm. broad. The 
stalk is straight, 7 mm. thick at the point of origin and broken off at a distance 
of 9 cm. from the sponge-body. Although, as above stated, the upper part of 
the sponge is much torn, one can make out in the middle of it a nearly cylindrical, 
terminally rounded gastral cone about 10 mm. thick, connected by four radial, 
vertical, membraneous plates joining it with the gastral wall. The surface 
appears very rough and uneven. This is doubtlessly due to the loss of the dermal 
membrane. 
The three specimens of form C are cake-shaped. Of their dermal mem- 
branes and the stalks only slight remnants remain. The best preserved one 
(Plate 41, figs. 13, 14) is a stout, marginally rounded disc, broad-oval, nearly 
■circular in outline. It measures 66 mm. in length, 60 mm. in breadth, and 27 mm. 
in thickness (height). The lower face is nearly flat, the upper convex. The 
centre of the latter is occupied by a gastral depression 20 mm. in diameter, 
nearly circular in outline, and surrounded by a circular wall on the margin of 
which remnants of a thin frill can be made out. Where this frill is best preserved 
it appears to be turned outward. A low, dome-shaped, gastral cone about 6 mm. 
thick arises from the centre of the depression. This cone is connected with the 
gastral wall by four vertical,' radial membraneous plates. The wide spaces 
between these radial plates appear as diverticular parts of the gastral cavity, 
which are continued down into the interior of the sponge. A few stalk-spicules, 
