(JEODIXELLA ROBUSTA. 213 



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

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

 everjf respect similar to those of var. carolae, the only difference being that their 

 rhal)domes, which measure 1.4-2.1 mm. in length, are on an average sHghtly 

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

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

 sometimes attaining a thickness of 42 ^t. The clade which is terminal (Plate 1, 

 fig. 14), or, more rareh', 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 

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



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

 derivates with more than one cladome are rare. I have observed 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 monoclade 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 

 telocladcs with terminal clades reduced to mere rounded protuberances pass, 

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

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

 tlerivate tylostyles the tj-le 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 lying in the tyle was not con- 

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

 teloclade-derivates with clades further reduced are 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 s])onges 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 spicides, which, as stated above, are met 

 with occasionally in the spicule-preparations, are 8-12 p. thick. The longest 

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



