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



Subgenus 1. Htjalonema, sens, strict. (Pis. XXVII. -XXIX.; PI. XXX. figs. 9-17; 



PI. XXXIII. ). 



The superior aperture of the gastral cavity is covered by a sieve-plate, which extends 

 from the side (with its annular, cufi-like fringe of fine marginalia) either right across 

 the mouth of the cup, or sunk down into the latter, towards the inner surface, in funnel- 

 shaped fashion. 



1. Hyalonema sieholdii, Gray (PL XXVII. figs. 1-13). 



Among the numerous species of Hyalonema obtained by the Challenger Expedition, 

 the familiar Japanese form, Hyalonema sieholdii, Gray, one of the best and first known 

 Hexactinellids. was unfortunately not included. A collection of Japanese Hexactinellids, 

 however, entrusted to me by Dr. Doderlein, contained a tolerably well-preserved dried 

 specimen of this sponge, which is figured after a photograph (one-third natural size, not 

 one-half as stated on the plate) on PL XXVII. fig. 1. I was able further to compare 

 this with several di'ied and preserved specimens in the Royal Museum, Berlin, which 

 were brought from Japan by Dr. Hilgendorf. 



The total length of the specimens examined varies from 50 to 80 cm. The body 

 proper measures 6 to 15 cm. in thickness, and occupies 10 to 15 cm. of the above total 

 length, the remainder representing the length of the spirally twisted, basal tuft. The 

 upper portion of the latter where it joins the body, and where, for a distance of 10 to 20 

 cm., it is beset by Palythoa fatua, M. Schultze, only attains a diameter of 5 to 10 mm. 

 Gradually, however, the tuft becomes looser, and breaks inferiorly into a bushy bundle. 

 Since the form and external appearance of the whole sponge have been already described 

 and figured in detail by Max Schultze and others, I shall simply restrict myself to 

 emphasizing the important points, and devote more attention to certain structural 

 relations which have been hitherto less intimately investigated. The general form of the 

 body is cylindrical, transversely truncated at the upper end, and inferiorly narrowed in a 

 somewhat conical manner, rounded off, and finally ending in a small inconspicuous 

 marginal pad. The superior external margin bears a fine fringe, composed of slender 

 needles projecting in wreath-like arrangement (marginalia). The upper truncated surface 

 is formed by a sieve-plate, which is stretched right across, or protrudes with a slight 

 convexity. The component lattice-work of the sieve-plate is not, however, uniformly 

 developed, but is usually divided into four distinct portions by four zones of unperforated 

 membrane, which unite in the centre to form an irregular cross. The dividing zones 

 measure from 3 to 10 mm. in breadth, and the four irregularly triangular or roundish 

 perforated sieve portions vary in width from 2 to 4 cm. Each of the four perforated 

 sieve-regions corresponds to an equal sized, deep portion of the gastral cavity, while the 



