SPONGES — WHITELEGGE. 501 



The skeleton consists of a series of stout primary fibres ; they 

 are longitudinally arranged, and present a very wavy outline ; 

 they exhibit a few scattered, echinating, spined styli, and an 

 axial core of from two to six or more stout smooth styli ; they are 

 usually about 0-15 mm. in diameter and 0-35 mm. apart; the 

 secondaries are about 0-1 mm. or less in diametei", and the spicular 

 core appears to be increased in size as the surface is approached ; 

 each fibre terminates in a. divergent tuft of from six to twelve 

 acutely pointed styli ; the connecting fibres are mostly uni- or 

 bispicular, with only a trace of spongin ; the length of the 

 spicule evidently regulates the distance between the stouter 

 fibres ; frequently a solitary spicule may be seen ensheathed 

 in a scarcely perceptible layer of spongin, and yet it exhibits 

 from one to three or four echinating styli. 



The mesh is rather variable and may be round, oval, or sub- 

 rectangular ; this is due to the spreading of the spongin at the 

 points of origin or union of the fibres ; the average diameter 

 is about 0'3 to 35 mm. 



Megascleres ; — (1) Echinating spined styli, which are very 

 irregularly distributed and usually are about half their length 

 apart on the more slender fibres, but on the primaries they are 

 widely separated. The base is slightly swollen ; the shaft is 

 faintly spined and rapidly tapers from the middle to a long, 

 smooth, acute point; size 035 by 0008 mm. 



(2) Slightly curved, stout, smooth styli, with a well rounded 

 base and a long acutely pointed apex ; these are chiefly confined 

 to the fibres ; size 0-3 to 0-4 by 0-022 to 0-024 mm. 



(3) Slender*, smooth, cylindrical styli ; abundant in the dermal 

 layer as radiating tufts, and also scattered between the fibres ; 

 the base is often perceptibly enlarged and is generally tipped 

 with a series of minute spines ; the apex terminates in an abrupt 

 acute point ; size 0-2 to 0-3 by 0-0045 to 0-005 mm. 



Microscleres : — (1) Small toxa 0-04 by 0-0025 mm. (2) Large, 

 stout, bow-shaped toxa, size O'll by 0-04 mm., both forms are 

 abundant everywhere, except in the epidermal region and the 

 axis of the fibres. (3) Small isochelse fairly plentiful throughout 

 the sponge; size 0-02 mm. This form approaches Glathria 

 angulifera, Dendy, in some of its characters, but the habit and 

 the size of the spicules differ greatly. 



RHAPHIDOPHLUS, Ehlers. 



RHAPHIDOPHLUS TENEBRATUS, sp. nov. 



(Plate xlv., fig. 19.) 



Station 48. 



Sponge with a slightly expand base, and a short peduncle, 

 from which arise a series of parallel branches ; they are more or 



F F 



