CAULOPHACUS SCHULZEL 
51 
stalk are quite similar. Nearly all the pinules are regularly hexactine. There 
are numerous forms of microscleres. These can be classified in two groups not 
connected by transitions. The first group comprises hexasters, hemihexasters, 
and hexactines, the rays (end-rays) of which are, when young, smooth, and 
sharp-pointed, when adult covered with numerous large lateral spines and 
crowded with a verticil of terminal spines. The young forms of this group 
appear as oxy-, the adult forms as disco-hexasters, -hemihexasters and -hexac- 
tines. The second group comprises discohexasters with generally smooth 
main-rays, from the ends of which arise regular verticils or bunches of slender 
end-rays. The end-rays are densely covered with small lateral spines, and 
crowned with a verticil of terminal spines. The spicules of this group appear to 
replace, in this and other species of Caulophacus, the plumicomes of Sympagella 
and Calycosilva. For this reason and because they differ very considerably from 
the discohexasters of the other group of microscleres I think it better not to 
describe them as discohexasters, as previous authors have done, but to give them 
another name, discocomes. 
The discohexasters, etc., occupy the choanosome in dense masses. One 
of the rays of those situated in the walls of the large choanosomal canals is 
usually directed canalwards and protrudes into the canal-lumen. The walls 
of these canals therefore appear somewhat spiny and the spicules rendering them 
so might be considered, to a certain extent, as canalaria. 
The discocomes are met with chiefly in the subdermal and the subgastral 
region, and here occasionally form clusters in which large and small ones are 
irregularly intermingled. 
The rhabds of the stalk (Plate 10, figs. 11, 12) are 14-28 /x thick near the end. 
The end itself is more or less thickened. This terminal thickening is greater 
in the stout, than in the slender rhabds. When great it gives to the rhabd- 
termini the appearance of oval tyles. The thickened end-part (tyle) measures 
18-38 m in transverse diameter, and is 4-12 ^ thicker than the adjacent parts of 
the spicule. This more or less thickened end-part is densely covered with small 
spines; the remainder of the spicule is smooth. The terminal region occupied 
by the spines is 44-60 /x long. 
The rhabds of the body proper (Plate 10, figs. 1-7, 9, 10) are more or less, 
sometimes very considerably curved, slightly attenuated toward the rounded, 
usually somewhat anisoactine ends, centrotyle, and everywhere smooth, except 
at the ends. The end-parts are covered with small spines, and sometimes slightly 
thickened. These rhabds are 1. 2-4.3 mm. long, measured along the chord 
