UEPORT ON THE MONAXONIDA. xxi 



remain connected with it as " fimbriae " (Cladorhiza tridentata, Jigg. cltt.), and 

 so on. 



5. Bipocilli (woodcut, Fig. V., 7) ; these are curious forms which, owing to their 

 minute size, it is very difficult to make out satisfactorily. They occur only ia a 

 single genus, lophon. Each consists of a shaft, with a termiaal, cup-like expansion at 

 each end. A modification of this type of spicule, which occurs in a new species of 

 lophon, lophon chelifer, nobis (PI. XVII. fig. 3), has the cup-like expansions divided 

 into teeth, and thus seems to connect the bipocilli with the chelate forms. 



C. Stellate Forms. 



Microsclera of the stellate group are rare amongst Monaxonid sponges. In the 

 Tetractinellida and in the Tethyse they are, however, met with in great abundance and 

 under a great variety of modifications. We shall describe here only those types which 

 are certainly known to occur in the Monaxonida. 



^-^^Jl^^^ijli^^^cvs^ 



Fig. VII. — Stellate forms of microsclera. 



1. Spirulse (woodcut. Fig. VII., 1, la); these ai'e more or less elongated, spiral or 

 subspiral forms, which may be either smooth or provided with more or less numerous 

 spines. The spinose forms are very characteristic of the genus Spirastrella. 



2. Discastra (woodcut. Fig. VII., 2) ; spicules with a straight, elongated shaft, 

 usually with a spinose base, and surrounded by a greater or less number of usually 

 spinose whorls, altogether much resembling a miniature chess-man, or, in some species, 

 a little fir tree. These spicules occur in the genus Latruncidia. 



3. Amphiastra, consisting each of a cylindrical shaft bearing a single toothed whorl 

 at each end ; occurring, for example, in Axoniderma mirabile, nobis (PI. XXI. fig. 9). 



{h) The Spongiu, the Spon go blasts and the Connective 

 Tissue Sheath of the Skeleton Fibres. 



Before proceeding to treat of the arrangement of the skeleton it is necessary that 

 we should first speak of a second very important constituent thereof, viz., the spongin. 

 The spongin is the horn-like cementing material which, in many, though by no 



