^36 THE VOYAGE OF H.M.S. CHALLENGER. 



Spicules. — (a) Megasclera ; smooth, rather slender styli (PI. XLV. fig. 9), hastately 

 pointed and often slightly crooked; size about O'G by 0*014 mm.; often with slight 

 irregular inflations on the shaft. In the Kerguelen specimen these spicules are a trifle 

 shorter and stouter, and there occur also a very few, apparently abnormal, much larger 

 forms. (6) Microsclera; discastra, the "chess-man" spicules, which in this species 

 resemble in form miniature fir trees (PI. XLV. figs. 9«, 9&, 9c) ; each spicule is composed 

 of an expanded, spinose base, followed immediately by a rather irregular whorl of separate 

 short spines ; then comes a short, stout, smooth, cylindrical shaft which suddenly expands 

 into a broad, flattened, circular whorl with denticulated margin ; three of the indentations 

 are so deep as to cut right down to the shaft, thereby dividing the circle into three 

 distinct segments (PL XLV. fig. %). This is much the largest of the whorls, and is 

 followed by three or four others gradually lessening in size till they end in a few small 

 spines on the shaft. The shaft itself is produced into a long, smooth, terminal portion, 

 gradually tapering to a fine point, and sometimes curved. Total length of spicule about 

 0"126 mm., of which the apical prolongation may form nearly half; diameter of largest 

 whorl about 0'044 mm. 



The most characteristic feature about this species, and that from which the specific 

 name has been derived, is the apical prolongation of the discaster, by which it may at 

 once be distinguished. The geographical distribution is very interesting ; we have, 

 during the course of our description, indicated various slight difi'erences between the 

 specimens from the two localities, but there is nothing to justify us in separating 

 them specifically. Details regarding the minute anatomy will be found in the Intro- 

 duction. 



Localities. — Ofi" Christmas Harbour, Kerguelen, January 29, 1874; depth, 70 

 fathoms. One specimen. 



Station 320, February 14, 1876; lat. 37° 17' S., long 53° 52' W.; ofl" the 

 mouth of the Eio de la Plata ; depth, 600 fathoms ; bottom, green sand ; bottom 

 temperature, 3 7° '2. Two specimens. 



Lat7-unculia hrevis, Eidley and Dendy (PI. XLIV. fig. 5 ; PI. XLV. figs, 10, 10a). 



1886. Latrunculia hrevis, Eidley and Dendy, Ann. and Mag. Nat. Hist, ser. 5, vol. xviii. 



p. 492. 



Sponge (PI. XLIV. fig. 5) massive, sessile, usually attached by the base to some 

 foreign object, and with more or less convex upper surface beset with numerous conical 

 processes. The best specimen in the collection is attached by a narrow base to a 

 fragment of Sporadopora ; it is about 63 mm. in diameter, and the upper surface is 

 rather flattened and thickly covered with the conical osculum-bearing processes, which are 

 aliuut 6 mm. in height. Colour in spirit yellowish-grey. Texture fairly compact 



