178 



Triptolemus incertus, sp. n. 

 Plate iv., tig8. 4 and ia-1. 



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

 skeleton of a specimen of Discodcrniia natalensis mihi. A 

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

 the larger incurrent and excurrent canals more or less tilled up 

 with centrotriajnes of all sizes. The only other spicules proper 

 to this species of Triptolemus are small curved, smooth microxea 

 and very minute metasters, the latter being rare. 



Spicules. Megascleres. — -Centrotricienes 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 A*, straight, 

 pointed; protocladi 180, deuterocladi 90. 



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

 smooth, curved, sharp-pointed. 



Metaster, total length including spines, 10 /*. 



There are four known species of Triptolemus, viz. : T. intextus 

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

 T. intextus has microxeas bearing blunt spines ; the centrotriaenes 

 are only 180 m, those of T. incertus being 500 m; on the 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 centrotriaMu- of T. cladosus is 

 only 142 ^. 



The habitats of the four species are as follows : — 



Triptolemus intextus Cr. on a Lithistid (Condlides howerhankii) 

 from St. Vincent, 374 fathoms. 



T. parasiticus, on a specimen of Carpenteria ; habitat un- 

 known. 



T. cladosus Sollas, found with a Lithistid, Condlistes thomasi, 

 from near the Ki Islands, 140 fathoms. 



T. incertus mihi, Cape \'idal, Natal coast, bearing X.N.E. 

 \ N., distant 9^ miles; depth, 80-100 fath(Miis ; bottom, rock; 

 burrowing in a Lithistid (Discodermia natalensis mihi). 



Note on Tetilla cnsiila (Carter). 



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

 Station living specimens of the peculiar hemispherical spon.^c with flat under 

 surface {Tetilla casula. Carter). This form seems to he an adaptation to prevent 

 sinkinji into the sand, as the animal in the tank remained ste.idily on the surface 

 of the sand on which it was placed." 



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

 Museum by Dr. Gilchrist was <,'iven in the first part of " Descriptions of South 

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

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

 protri^enes). Some species of Tetilla (T. polvara, T. euplocamus) are spherical 

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

 spherical and free or hemispherical and fixed. 



