178 



Triptolemus incertus, sp. n. 

 Plate iv., figs. 4 and 4a-f. 



Description. — The sponge burrows in the canals of the dead 

 skeleton of a specimen of Discodennia natalensis mihi. A 

 section of the Discodennia (Fig. 4, between the crosses) shows 

 the larger incurrent and excurrent canals more or less filled up 

 with centrotria^nes of all sizes. The only other spicules proper 

 to this species of Tripfoleniiis are small curved, smooth microxea 

 and very minute metasters, the latter being rare. 



Spicules. Megascleres. — Centrotriaenes of various sizes, the 

 cladi being simple or branched one, two, or three times, usually 

 dichotomously, but sometimes into three branches not in the 

 same plane ; frequently the final branches are curved. 



Dimensions of a large spicule: rhabdome 310/', straight, 

 pointed; protocladi 180, deuterocladi 90. 



Microscleres. — Microxea, 100x3 '^ ^^ 180x4 ''- fusiform, 

 smooth, curved, sharp-pointed. 



Metaster, total length including spines, 10 z'. 



There are four known species of TnptoJcmus, viz. : 7". intexfus 

 Cr., T. parasiticus Cr., T. cladosus SoUas, and the present form. 

 T. intexfus has microxeas bearing blunt spines ; the centrotriaenes 

 are only 180 /*, those of T. incertus being 500 m; on thje other 

 hand, the amphiasters of Carter's species are 100 m in length. 



Sollas's species contains both smooth and trichose microxeas; 

 and the centrotriaenes do not attain to such a size as those of 

 T. incertus. 



The total diameter of a large centr()tria?ne of 7". cladosus is 

 only 142 M. 



The habitats of the four species are as follows : — 



Tripfoleuiiis iutcxtus Cr. on a Lithistid (CoraUiies howerhaiikii) 

 from St. Vincent, 374 fathoms. 



' T. parasiticus, on a specimen of Carpenteria ; habitat un- 

 known. 



T. cladosus Sollas, found with a Lithistid, Condlisfes tJio>nasi, 

 from near the Ki Islands, 140 fathoms. 



T. incertus mihi. Cape Vidal, Natal coast, bearing N.N.E. 

 I N., distant 9^ miles; depth, 80-100 fathoms; bottom, rock; 

 burrowing in a Lithistid (Discodennia natalensis mihi). 



Note on Tctilla casiiln (Carter). 



Dr. Gilchrist writes to me : — " We now have in the tanks of our Marine 

 Station livinj^ specimens of the peculiar hemispherical sponge with Hat under 

 surface (Tctilla cnsiiln, Carter). This form seems to be an adaptation to prevent 

 sinking into the sand, as the animal in the tank remained steadily on the surface 

 of the sand on which it was placed." 



A brief description with figures of a specimen of this species sent to the 

 Museum by Dr. Gilchrist was given in the first part of '' Descriptions of South 

 African Sponges." The circular flat under surface of the hemisphere had a 

 satiny smoothness, and was surrounded by a fringe of spicules (oxeas and 

 protrirenes). Some species of Tctilhi (T. polyara, T. euplocamus) are spherical 

 or ellipsoidal and provided with a tuft of anchoring spicules ; others, again, are 

 spherical and free or hemispherical and fixed. 



