R. KIRKPATRICK. 



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

 arrangement 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/i in length. 



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

 and 270/i in thickness in the middle. 



The basalia (IV. 3a, a 1 ) 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 pentactiu 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, 



