c;rodinetj>a robusta. 



213 



or plagio- or pro-monaenes (Figs. 5-9, 11). The latter are much more numerous 

 than the former. The monaenes of var. megasterra (Figs. 1-4, 18-20) are in 

 every respect simihir to those of var. carolae, the only difference being that their 

 rhabdomes, which measure 1.4-2.1 mm. in length, are on an average slightly 

 longer. The monaenes of var. megaclada (Plate 1, figs. 13, 14; Plate 4, fig. 23) 

 have rhabdomes similar to those of the monaenes of var. megasterra but thicker, 

 sometimes attaining a thickness of 42 /«. The cladc which is terminal (Plate 1, 

 fig. 14), or, more rarely, situated a little below the end of the rhabdome (Plate 1, 

 fig. 13; Plate 4, fig. 23), is conic, pointed, 80-105 /« long, and straight or slightly 

 bent upwards at the end. It encloses an angle of 87 135° with the rhabdome. 



The teloclade-derivates (Plate 1, fig. 15; Plate 4, fig. 25). The teloclade- 

 derivates with more than one cladome are rare. I have ol^served them only 

 among the monaenes, and they never seem to have more than one secondary 

 cladome. The primary (terminal) clade is similar to that of ordinary mo- 

 naenes, the secondary clade is situated a considerable distance below the 

 cladomal end and smaller than the primary clade (Plate 1, fig. 15). The 

 mesoclades are likewise rare. They are always monocladc and appear as rhabds, 

 attenuated towards both ends or towards one end only with a short and stout 

 clade arising a considerable distance from either end (Plate 4, fig. 25). The 

 teloclades with terminal clades reduced to mere rounded protuberances pass, 

 by further cladome-reduction, into tylostyles and styles. They appear as 

 transitional forms connecting the teloclades with the rhabds. In the teloclade- 

 derivate tylostyles the t} lc is often irregular and the axial thread of the rhabd- 

 ome becomes tortuous on entering the tyle. In one of these spicules I noticed 

 that the short, tortuous part of the axial thread l,ying in the tyle was not con- 

 nected with the axial thread of the rhalxlome. Mesoclade and multicladomal 

 teloclade-derivates with clades further reduced arc rare. They pass into the 

 rhabds with one or more protuberances or annular thickenings (Plate 4. figs. 

 6, 7). These resemble the rhabds proper so closely, that I have thought it 

 better to describe them above together with the regular rhabds. 



The shape, size, and arrangement of the megascleres of these sponges and 

 the closeness of their connection by transitional forms lead to the conclusion 

 that the rhabds are more closely related to the teloclades than is generally 

 assumed. 



The fragments of long and slender spicules, which, as stated above, are met 

 with occasionally in the S])icule-preparations, are 8-12 /( thick. The longest 

 one observed was over 2 mm. in length. Most of them are broken off at both 



