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



fringe of spicules on the somewhat sharpened, oscular margin of the gastral cavity. On 

 the outer surface of the body, between the radial groups of spicules, one can see the 

 characteristic network formed from the tangential rays of the hypodermalia, while on the 

 inner surface of the gastral space irregular groups of closely adjacent, minute, circular 

 apertures (0'5 to 1 mm. in diameter) penetrate, like sieve pores, the somewhat uniform, 

 curved, smooth wall. In the parenchyma, I have only been able to find quite isolated, 

 laro-e and middle-sized hexacts. Beside the long, radial rays of the large hypodermal or 

 liypogastral pentacts, a great number of various diacts occur, and small oxyhexacts in 

 special abundance. The latter are for the most part long and slender, but in part also 

 comparatively short. Only a few are smooth ; most of them bear somewhat closely 

 apposed spines turned in the same direction. They may perhaps be thus best described 

 as uncinates. Others occur in which the long, median portion is smooth, but the ends 

 beset with spines. 



Some of the very long, slender uncinates, which usually occur in bundles, bear several 

 simple, obliquely projecting, or almost apposed bars ; while others exhibit, below each 

 slender pointed, almost appressed spine, a minute, longitudinal furrow or rib, as has 

 been figured by Wyville Thomson in Pheronema carpenteri (loc. cit., pi. Ixviii. fig. 4). 

 The short and rather thick uncinates have on an average a length of only 0"5 to 1 mm., 

 and bear spines of very varied length, and occasionally quite rudimentary (PI. XLII. 

 fig. 6). 



The small oxyhexacts have an average diameter of 0'14 mm., and are characterised by 

 transverse, rather blunt, externally directed, slender and somewhat bent spines, longest 

 in the middle of the rays, and decreasing towards the ends (PI. XLII. fig. 12). 



The very strongly developed dermal skeleton exhibits strong hypodermal oxypentacts 

 with long smooth rays, which are not however always at right angles to one another. 

 The proximal radial ray is indeed usually at right angles to the four tangentials, but these 

 frequently form acute or obtuse angles, or are bent near the point of intersection into 

 the tangential plane. The rays of these large smooth oxjqientacts are as a rule straight, 

 but slight curvatures not unfrequently occur, either in simple or in 3- shaped fashion. 



The pinuli of the external skin are moderately large oxypentacts, with four rather 

 long, slender, tangential bases, which are rarely quite smooth, in fact, usually beset with 

 more or less long, oblique, externally directed spines. The oblique somewhat externally 

 bent spines of the more or less long free distal ray vary in abundance. They sometimes 

 produce an almost bushy appearance, and are longest in the middle of the ray (PI. XLII. 

 fig. 10). The dermal ampliidiscs vary greatly in size and form. The largest are 

 between 0'2 and 0"3 mm. in length, and exhibit a strongly developed axial rod with 

 hemispherical tubercles and expanded campanulate umbels with eight smooth lancet- 

 shaped umbel rays (PI. XLII. fig. 2). Besides these, numerous amphidiscs of medium size 

 occur, measuring 0'05 to O'l mm. in length, with a slightly tuberculate axial rod and eight 



