HYALONEMA (HYALONEMA) OBTUSUM. 159 



long, usually 45-70 n, at the base 4.5-5.5 ix thick, rarely as much as 6 m, conic, 

 pointed or, more rarely, rounded at the end, and covered with spines, which are 

 more conspicuous in the distal than in the proximal portion of the rays. In 

 the gastral pinules of var. rohusta the lateral rays are on an average somewhat 

 longer, they measure here 47-75 y. in length. 



The marginal pinules (Plate 36, figs. 10-13, 26-28) have been found only in 

 var. gracilis; in the specimen of var. rohusta they appear to have been lost. In 

 these pinules only the distal and proximal rays are properly developed, the lat- 

 eral rays being altogether rudimentary, and together forming merely a tyle. 

 These spicules consequently appear as centrotyle diactines. The outer, distal 

 one of their two properly developed rays, which corresponds to the distal apical 

 ray of the hexactine and pentactine pinules, is 304-300 ^ long, rarely as much 

 as 450 IX, fairly straight, and 5-10 tx thick at the base. Its proximal part, and its 

 distal, conic, sharp-pointed end-part, are smooth. Its middle-part bears spines, 

 which are rather strongly inclined towards the end of the ray, attain 6-10 ai in 

 length, and are 1.5-2 n thick at the base. The maximum transverse diameter of 

 this ray, together with the spines, is 17-20 //. 



The opposite, inner, proximal one of their two properly developed rays, which 

 corresponds to the proximal apical ray of the hexactine pinules, is usually 490- 

 665 n long, fairly straight, at the base about as thick as the distal ray, and 

 attenuated towards the end. Sometimes it is greatly reduced in length, only 50 ix 

 long, cylindrical, and thickened at the end to a terminal tyle 13 ix in diameter. 



The central tyle, which is all there is left of the reduced lateral rays, is 3-7 ix 

 thicker than the adjacent parts of the spicules, and measures 8-15 m in transverse 

 diameter. 



The hypodermal pentactines of the outer surface (Plate 33, figs. 5-14, 17, 24; 

 Plate 34, fig. Ic; Plate 39, figs. 31, 32, 40, 41). The proximal apical ray is 

 straight or, rarely, slightly curved, and usually properly developed, conic, and 

 blunt-pointed, occasionally reduced, cylindrical, and terminally thickened 

 (Plate 34, fig. Ic). It is in the large hypodermal pentactines, which greatly pre- 

 dominate in the upper parts of the specimen of var. gracilis, when properly de- 

 veloped, 0.7-1.86 mm. long and, at the base, 30-75 /x thick, rarely 90 ix. When 

 reduced it retains its thickness throughout, but is less than half as long. In the 

 small hypodermal pentactines, which occur chiefly in the lower part of this 

 sponge, the proximal ray measures 0.27-0.6 mm. by 10-23 ix. The lateral rays 

 are inclined towards the proximal ray, and enclose with it angles of 73°-84°. 

 The four lateral rays of the same spicule are usuallj^ very unequal in length ; the 



