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



The outer covering of the trunk up to the collar is thickly beset with spicules, which, 

 placed close together, form a continuous sheath. These spicules consist, in the more 

 simple cases, of short thick spindles covered with long and usually branched curved 

 spines placed in several circles. They are 0'3 mm. long and 0'13 mm. in diameter. 

 They are frequently bent and then the convex side is covered with longer spines, like 

 the spicules of many Muriceids ; length 0*28 mm., diameter 0-07 mm. There are also 

 club-shaped spicules, whose thicker end is covered with branched prickly spines ; size, 

 0*25 by 0'15 mm. and 1'8 by 0'08 mm. There are, further, double forms, in the 

 shape of a cross, whose rays bear jagged, branching spines; diameter 0"32 mm. The 

 branching spines serve to unite the spicules together by interlocking with one another, 

 and thus to form a continuous armature. Above the collar these forms disappear, 

 and in their place long bent spindles occur in the mesoderm. These are usually 

 placed at right angles to' the long axis of the stem and branches, in which they 

 alone occur. Their length reaches 2 to 4 mm. Spaces filled with soft skin are left 

 between them, so that here the outer covering is flabbier than in the lower part of the 

 trunk. 



In the finer twigs these spicules are arranged longitudinally and pass into the 

 peduncles of the polyp heads, beyond which they project in the form of fine spines. 

 These spicules are spindle-shaped, they are often bent so as to become /"-shaped and 

 truncated at one end ; they are covered all over with fine spines. They measure 0"8 

 by 0-04 mm., 2 by 0-07 mm., 4 by 0-09 mm.; the latter in the bundle of spicules sur- 

 mounting the head. 



The peduncle of the polyp head is heavUy armed with large /-shaped spicules. 

 The polyp head is surrounded by larger and smaller spicules which radiate from the 

 base to the margin, beyond which eight of them project like spines. These are bent 

 and truncated at the base, or forked and completely covered with sharp little spines. 

 They measure 0-8 by 0-5 mm., 07 by 0-038 mm. The smaller spindles, which are 

 either straight or bent, measure 0*26 by 0-03, 0-3 by 0*02, 0-3 by 0-025 mm. Small 

 spicules occur embedded in the tentacles. 



The colour of the stem and of the branches and secondary branches is white ; that 

 of the terminal twigs and polyps, as also of their spicules, is purple. The polyps of the 

 collar are bright red, in one case white. The tentacles are white. 



Habitat.— Station 192, off the Ki Islands ; lat. 5° 49' 15" S., long. 132° 14' 5" E.; 

 depth, 140 fathoms ; bottom, blue mud. 



Spongodes heterocyathus, n. sp. (PI. XXXVId. figs. 3a, 3b). 



The colony consists of a globular head formed by the rapid ramifications of a short 

 stem, whose terminal twigs bear bundles of polyps. One. larger polyp, of special 



