== i694 = 
Dermal spicules of Lithistids. 
(Plate III, figs. 11, 12, 15). 
Compound trifid spicules with relatively short, straight 
or slightly curved, pointed shaft and with spreading head- 
rays. There are three forms of these spicules, small in com- 
parison with the trifid spicules belonging to Geodia, and 
probably belonging to different species of sponge. The first 
(fig. 11) has the shaft curved and the primary head rays 
also curved and directed upwards; they bifurcate into very 
small pointed secondary rays. An average spicule is 0,675 mm. 
in length and the thickness of the shaft 0,056mm. In the 
second form (fig. 12) the shaft is straight and pointed, the 
primary head rays are very long in proportion to the shaft 
and directed forward and the secondary rays are similarly 
long, divergent, and projecting upwards. Total length of the 
specimen figured 0,787mm. diameter of shaft 0,045 mm. ; 
width across head rays 0,675 mm. This form has been found 
also in the Irish Chalk, (Wright: op. cit. Pl. Il, fig. 16). The 
third form (fig. 15) has also a straight shaft but the rays are 
very short and pointed, and they bifurcate so close to the 
top of the shaft that the primary ray can scarcely be distin- 
guished. The length of the specimen figured is 0,99 mm. 
thickness of shaft 0,056 mm. 
As regards their dimensions, these spicules correspond 
much closer with the trifid spicules which are present as 
surface spicules in different genera of Lithistid sponges, than 
with the trifid zone spicules of Geodia, and it seems to be 
very probable, that they are allied to the surface spicules of 
Corallistes, O. Schmidt. 
Dermal? spicule of Lithistid ? 
(Plate I, figs. 29, 30) 
Spicule consisting of a slender, more or less elongated, 
nearly cylindrical shaft, having at one extremity four elongated 
