8 E. KIRKPATRICK. 



to the presence of a worm-tube in the wall of the sponge, thereby leading to a dis- 

 arrangenaent of the pleuralia and velum. 



The'gastral cavity is capacious, and is lined by a continuous gastral membrane. 

 The wall of the sponge is about 2 cm. thick. The spicules, with certain exceptions, 

 resemble those of specimen C described below. 



Specimen C. — (Plate I., figs. 3, 4 and pi. IV., figs. 3a-3l, excepting 3h). 



This is a remarkable twin specimen, ovate spheroidal in shape, and with two oscules. 

 The height is 14 cm. and width 19 cm. The massive, dense root-tuft is 5"5 cm. in 

 length. The edges of the oscules are slightly inverted, so that the innermost margi- 

 nalia, projecting 2' 5 cm., slope downwards and inwards. A vertical section through 

 the line joining the oscules shows the sponge body, apart from the massive root-tuft, 

 to be somewhat hour-glass-shaped with the long axis horizontal. 



The common gastral cavity is nearly divided into two by a thick, central, 

 pyramidal boss reaching from floor to roof, but not forming a complete partition. 



The wall of the sponge attains in one part the great thickness of 3 ' 8 cm. The 

 gastral surface shows numerous circular orifices, from 1 to 3 mm. in diameter, in this 

 respect differing from other known specimens of this species, in all of which the 

 gastral surface is covered with a continuous layer. 



The twin condition of the specimen cannot be regarded as one of any specific 

 importance. Among the specimens of R. antarctica obtained by the ' Challenger ' 

 from 274 m. off Kerguelen Island is a twin specimen with a short common base 

 whence spring two thick cylindrical tubes ; the shape somewhat resembles that of a 

 gigantic tuning-fork. The gastral cavities communicate through an oval foramen 

 below, and the gastral membrane is continuous throughout. 



Spicules of Specimen C. — The principalia are diactins with rounded or 

 bulbous, roughened ends, and large regular hexactins with smooth tapering rays each 

 640/A in length. 



The marginalia are smooth, thick, fusiform diactins, about 4 cm. in length, 

 and 270)L(, in thickness in the middle. 



The basalia (IV. 3a, a^) are anchor pentactins with four prongs, usually curved, 

 but sometimes straight. Both in B and C these anchor spicules are present among the 

 hypodermalia some distance above the root-tuft, and some have the prongs anortho- 

 tropal, thus supporting Schulze's supposition that pentactin basalia are often modified 

 hypodermal pentactins. 



The autodermalia (IV. 3b.) are chiefly pentactins with or without a distal knob ; 

 hexactins being fairly common in B, but rare in C- 



The OXypentactin hypodermalia, as might be expected, are larger than in 

 specimen A, and have thicker rays with longer prickles. 



The autogastralia (IV. 3c) are mainly hexactins with spined, blunt-ended rays, 



