378 PROF. E. A. MIN^OHIN ON THE BRITISH [DcC. 13, 



at tlie distal extremity, but the curvature may be very slight, all 

 tlu-ee i-ays then being practically straight. The unpaired rays 

 vary from 65-83 /x in length and are about 6 or 7/i in thickness; 

 the paired rays range from 80-100 ju in length, with a breadth of 

 7 or 8^. (2) In most specimens thicker triradiates occur (text- 

 fig. 9G, fig. 21 c, p. 381) with the anterior angle approaching 180°, so 

 that the spicule appears nearly T-shaped. The paired rays, seen 

 in facial aspect, may appear nearly straight, but more usually the 

 proximal backward curve of the ray is short, while the distal 

 forward curvature extends over moi-e than half the length of the 

 ray. The system as a whole is strongly concave on the gastral 

 face, so that when seen in facial asj^ect from the gastral side one 

 of the two paired rays is usually very much foreshortened, and 

 therefoi'e appears different in length and curvature from the 

 other. The rays reach 10 ju in thickness. (3) In all specimens 

 peculiarly modified triradiates occur which may be termed brackets 

 (text-fig. 94, figg. lOy", \Qg, p. 377). The two paired rays are 

 straight or curved, and more or less normal as regards length and 

 proportions, though in some cases rather slender ; the unpaired 

 ray, on the other hand, is short and strongly curved out of the 

 plane in which the paired rays lie, so that in a facial view of the 

 spicule it is not in focus at the same time as the paired rays. 

 The unpaired ray is often irregularly curved, and may be reduced 

 to a mere knob or even to the vanishing point. (4) The ordinary 

 quadriradiates (text-fig. 94, figg. 10 A, 10 i, &c., p. 377) have the 

 basal rays similar to (1); the gastral ray is of moderate length, 

 smooth, and evenly curved at the tip. (5) The thickened T-shaped 

 triradiates, as in (2), may develop a gastral ray, which is then 

 rather thick and set very upright on the basal system (text-fig. 94, 

 fig. 11 c, p. 377 ; text-fig. 96, fig. 21 g, p. 381). (6) The brackets 

 may also bear a gastral ray, which is then usually of very great 



Explanation of Text-fig. 95 (opposite). 



Spicules of Leucosolenia variabilis. 



Figg. 14«-14/'. Spicules of a specimen fi-om Roscoff showing triradiates of un- 

 usually small size, a, h, triradiates ; c, quadriradiate ; d, e, curved monaxons ; 

 f, straight monaxon. — Figg. 15 a-lbf. Spicules of a specimen from Pljanouth 

 showing triradiate systems unusually large, a, h, triradiates ; c, quadriradiate ; 

 d,e, curved monaxons ; y, straight monaxon. — Figg. 16a-16^. Spicules of a 

 specimen from Bantry Bay, Ireland, in Norman's collection, identified by Haeckel 

 as Ascandra variabilis, a, triradiate ; b, c, quadriradiates ; d, bracket with 

 greatly elongated gastral ray ; e,f, curved monaxons ; g, bayonet-like monaxon. 

 — Figg. 17 a, 17 b. Bayonet-like monaxons of a specimen from a tide-pool below 

 the Hoe, Plymouth. — Figg. 18 a-18 e. Spicules of the specimen from Brighton 

 Aquarium figured by Bowerbank (' British Spongiadse,' iii. pi. xci. fig. 7) under 

 the name Leuoonia somesii (Brit. Mus. Bowerbank Coll. 1019). «, b, tri- 

 radiates ; 0, quadriradiate ; d, e, curved monaxons showing their great variation 

 in size. — Figg. 19 a-19 7i. Spicules of another of Bowerbank's specimens of 

 Leiiconia somesii {I. c. pi. xci. fig. 6) (Brit. Mus. Bowerbank Coll. 1017) show- 

 ing a tendency to develop abnormal forms of the triradiates and monaxons of 

 great length, irrespective of thickness, a-e, triradiates ; f-h, monaxons; h, on 

 account of its great length, has been drawn in two pieces. 



