1 904.] SPONGES OF THE GENUS LEUCOSOLEXIA, 365 



from 100 /Lt to 120 jti, the thickness about 6 /.t ; the paired rays 

 range from 75 /j. to 90 /.t in length, with a thickness of abovit 7 /i. 



(2) Besides the ordinary triradiates just described, there occur in 

 some specimens triradiates with shorter and more thickened rays 

 (text-fig. 91, fig. 2d-f, p. 364; text-fig. 93, fig. 7 c, p. 369). The 

 jji-oximal curve of the paired rays is scarcely noticeable ; while the 

 distal curve is rathei' accentuated. The length of the rays is about 

 70 /J. or rather more in some specimens, the thickness 9 or 10 /x. 



(3) The ordinary quadriradiates have the basal rays similar to (1) 

 and the gastral rays of moderate length, curving forwards at the 

 tip, smooth and tapering evenly to a point (fig. 1 i). The gastral 

 i-ay is implanted on the unpaired ray of the basal system, distinctly 

 behind the central point of the junction of the three rays compos- 

 ing it. In some specimens the quadriradiates are, on the average, 

 of slightly larger dimensions than the triradiates. (4) Occasionalh" 

 a gastral ray is found developed on the thickened triradiates (2), 

 but this is rather a rare type of spicule (text-fig. 93, fig. 7e, p. 369). 



(b) Monaxon Spicules. — Thi'ee kinds occur constantly, and are 

 the most diagnostic feature of the species. (1) Large spicules with 

 distinct lance-heads (text-fig. 91, figg. lo-lg, p. 364). The cylin- 

 drical shaft is always more or less curved, sometimes irregularly, and 

 tapers rather rapidly to a sharp point at the proximal extremity, 

 but at the distal end remains of even thickness or diminishes only 

 very slightly and almost imperceptibly up to the large, broad, sharp- 

 pointed lance-head. The length is usually from 190 to 280 yu, the 

 thickness 9 or 10 yu. (2) Large spicules without lance-heacls, be- 

 longing to the category of ref ringent monaxons (text-fig. 9 1 , figg. 1 on, 

 1 n, p. 364). These are generally fewer in number than (1), and 

 each is usually nearly straight or but slightly cvirved. The shaft 

 is thickest about one-fourth of its length from the proximal end, 

 whence it tapers rapidly to a point proximally and very gradually 

 to a sharp point distalh". Sometimes there is a slight indication 

 of a rudimentary lance-head distally, but ustiallj'^ there is none. 

 Length usually about 200 ;t<, greatest thickness 8 or 9 jj.. (3) Small 

 and slender spicules, usuall}- with no trace of a lance-head, and, 

 with rare exceptions, perfectly straight (text-fig. 91, figg. \j 

 to 1 I, &c.). The shaft is thickest close to the proximal end, 

 where it tapers rapidly to a point. From the region of greatest 

 thickness the shaft tapers extremely gradually to the very sharp 



Explanation of Text-fig. 91 (opposite). 



Spicules of Lettcosolenia complicata, 



Figg. la-1 q. Spicules of a quite normal specimen from Eoscoff, one of the same lot 

 as that figured in Lankester's 'Treatise on Zoology,' part ii.Porifera,p. 5, fig. 4. 

 a-d, triradiates ; e-i, quadriradiates ; J-1, slender monaxons ; m, n, large 

 monaxons without lance-heads; o-q, large monaxons with lance-heads. — 

 Figg. 2a-2 I. Specimen dredged on Duke Eock, Plymouth (Garstang), showing 

 thickened triradiates in addition to ordinary forms, a, ordinary triradiate ; 

 b & c, quadriradiates; d-f, thick triradiates; cf-i, slender monaxons; J, large 

 monaxon without harb ; I- & 7, large barbed monaxons. 



