230 THE VOYAGE OF H.M.S. CHALLENGER. 



Although I am not usually inclined to bestow specific distinction on such an imper- 

 fect specimen, it seemed to me justifiable to make an exception in favour of this form, 

 on account of the marked breadth and strength acquired by the larger almost spherical 

 amphidiscs, and also because of other peculiarities among the spicules. 



The large supporting spicules of the parenchyma are more or less long diacts 

 of variable strength, besides which isolated medium-sized, strong oxyhexacts also 

 occur, as also very aljundaut slimmer medium-sized oxyhexacts, in which the rays 

 are covered with slender spines inserted at right angles (PI. XXXII. fig. 8). Between 

 these a host of small smooth oxyhexacts with curved rays also occur (PI. XXXII. 

 fig. 6). 



The dermal skeleton contains strongly developed hypodermal oxypentacts with 

 proximal rays of variable length. On the tangential rays are inserted rows of autodermal 

 pentact pinuli, with four short, strongly developed tangential basal rays, beset with short 

 distaUy directed teeth, while the distal ray, about 0'3 mm. long, has a more bushy appear- 

 ance, due to somewhat long obliquely inserted spines which are specially weU-developed 

 on the median and external portions (PI. XXXII. fig. 7). Especially striking in the 

 dermal membrane are the very broad, almost spherical, strongly developed amphidiscs 

 (PI. XXXII. figs. 1, 2), with broadly arched terminal umbels which almost meet in the 

 middle. Each umbel consists of eight to twelve broad, paddle-shaped rays, which exhibit 

 a median ridge projecting inwards and rounded off terminally. They do not pass into a 

 terminal plate at the pole, but end sharply with a projecting margin round a central 

 circular pit (PI. XXXII. fig. 2). The opposed umbel rays are usually not exactly 

 ojjposite but alternating (PI. XXXII. figs 1, 2). 



Besides these, the dermal membrane contains other amphidiscs, with eight slender 

 umbel rays of smaller, and sometimes of much smaller size (PL XXXII. figs. 4, 5). The 

 small umbels only occupy a third of the total length of the amphidiscs, or even less in 

 the smallest forms (PI. XXXII. fig. 5). 



On the inner surface of the large internal cavity, in the gastral and canalicular mem- 

 brane, numerous amphidiscs occur of medium and small size. They exhibit in part the 

 same structure as those last described in the external skin (PI. XXXII. fig. 4), and in 

 part somewhat larger forms (PL XXXII. fig 3). Those large, almost spherical amphidiscs, 

 which occur so abundantly in the dermal membrane, are here altogether absent, nor have 

 I found any hj^ogastral pentacts or autogastral pinuli in the gastral or canalicular 

 membrane. 



In the lower portion of the body, which forms an annular pad, strongly developed 

 spicules with six to two cylindrical rays occur. Their rounded ends are beset for a 

 variable distance with teeth and spines (PL XXXII. figs. 9, 10), which often appear on 

 the rudiments of undeveloped rays (PL XXXII. fig. 10). 



