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



I ought not, however, omit to mention that in the Berlin Zoological Museum there is a 

 well preserved Hyalonema form, obtained from Sir Wyville Thomson, and labelled as 

 Hyalonema Itisitanicum, Bocage. This specimen figured in PI. XXXIV. fig. 1, does not, 

 however, in its form and in its spicules, resemble the Hyalonema of the British Museum, 

 but agrees in all essential points except size, with the Hyalonema thomsoni, Marshall. 

 I was therefore compelled to describe it under the latter designation. 



2. Hyalo7iema cebuense, Higgin. 



The species of Hyalonema which Higgin described in 1S75,* under the title Hyalonema 

 cebuense, is not represented among the numerous forms of the Challenger collection. 

 According to Higgin's account the form described must be a distinct species, and not — as 

 Carter seems inclined to make out in his remarks on Higgin's article — a mere variety of 

 Hyalonema sieholdii. The most important characteristics of the species are: — (l) the 

 peculiar sculp tor's-mallet-like form of the large body, which measures more than 1 4 cm. 

 in length and 12 cm. in breadth; (2) the strikingly thick and short, straight, smooth oxy- 

 diacts, which are said to belong to the dermal skeleton;" (3) the peculiar small parenchy- 

 mal oxyhexacts, which bear hook-shaped lateral spines at the ends of the rays ;^ (4) the 

 slim double-harpoon-shaped oxydiacts, bearing all along both rays curved teeth turned 

 towards the centre,* and finally (5) the presence of four blunt anchor teeth on the long 

 spicules of the tuft.^ 



It is not evident from Higgin's otherwise accurate and detailed description whether 

 a terminal sieve-net covers the gastral cavity, or whether the latter remains open, nor 

 does he note the presence or absence of a fringe of marginal sj^icules. From the fact 

 that no polype encrustation was observed on the upper end of the fibrous tuft, one 

 cannot of course certainly infer its absence during life, since it might readily have been 

 separated ofi". 



3. Hyalonema tenue, n. sp. (PI XXX. figs. 1-8). 



To the east of the mouth of the Rio de la Plata (Station 323, lat. 35° 39' S, long. 

 50° 47' W), from a depth of 1900 fathoms and a blue mud ground, two fragments of a 

 Hyalonema were dredged, the siliceous elements of which appear to me sufficiently 

 characteristic to justify the erection of a distinct species. One of the fragments has the 

 form of a thin irregular plate about 2 cm. square in the middle of which a normal oval 

 space, 6 mm. long by 4 broad, can be detected (PI. XXX. fig. 1). This opening is 



^ Ann. and Mag. Nat. Hist, ser. 4, vol. xv. p. 377. '^ Loc. cit., pi. xxii. fig. 1. 



3 Loc. cit, pi. xxi. fig. 5. « Loc. cit, pi. xxi. fig. 3. 



' Loc. cit., pi. xxi. fig. 9. 



