CAtJLOPHACUS SCHULZEI. 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., occi^^y 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 fi 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 n in transverse diameter, and is 4-12 yu 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 4^60 fx long. 



The rhabds of the body proper (Plate 10, figs. 1-7, 9, 10) are more or less, 

 sometimes very considerably cm"ved, 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 nmi. long, measured along the chord 



