98 BATHYDORUS LAEVIS SPINOSISSIMUS. 



with angles of 90° or less are to be considered as rhabd-derivates like those with 

 obtuse angles. 



In all these diactines the two rays are of equal thickness at the base. I 

 found, however, also an angularly bent diactine with an angle of 73°, in which 

 one ray, 460 n long and 7 n thick at the base, was curved concave towards the 

 other, the other being straight, 850 n long and 23 ix thick at the base. 



The pentactines and apparently pentactine-derivate hexactines. Among the 

 pentactines two groups can be distinguished, one with relatively long, and the 

 other with relatively short lateral rays. The hexactines appear to be derivates 

 of pentactines belonging to the first group. 



The pentactines with relatively long lateral rays (Plate 16, figs. 4-8, IG, 17, 

 20-24). The proximal ray is 0.5-1.5 mm. long, usually straight, conic, and 20- 

 38 fi thick at the base, and gradually attenuated to the blunt end, which meas- 

 ures 4-8 n in transverse diameter (Plate 16, figs. 4-6, 8). Rarely the proximal 

 ray is either curved, or nearly cylindrical, rounded, and slightly thickened at the 

 end (Plate 16, fig. 7). The lateral rays are generally straight, conic, and blunt, 

 those of the same spicule being usually not very different in length (Plate 16, 

 fig. 4). Sometimes, however, one of the lateral rays is either shghtly curved 

 (Plate 16, fig. 16) or greatly reduced in length, cylindrical, and terminally rounded 

 (Plate 16, fig. 17). The longest lateral ray of the pentactine is 270-750 ju long, 

 the shortest 60-700 /^. The lateral rays are usually about 2 n thinner at the base 

 than the proximal ray of the same spicule. Their ends are 2.5-15 n thick. The 

 lateral rays enclose angles of 76°-97°, usually considerably less than 90°, with the 

 proximal ray. 



In many of these pentactines all the rays are rather densely covered with 

 spines throughout their whole length (Plate 16, figs. 15, 20-23). These spines 

 are conic, sharp-pointed, about 1 ii high and, on an average, 4 n apart. Towards 

 the ends of the rays the spines usually become smaller and less numerous. The 

 ends themselves, however, generally bear considerably larger spines, which either 

 pass gradually into the smaller ones, or are separated from them by a distinct 

 limit, situated a short distance from the end of the ray. In some pentactines 

 the spiculation is not so great, portions of the rays appearing quite smooth. In a 

 few hardly any spines, or no spines at all, could be detected. 



When these spicules are slightly heated, the superficial silica-layers partly 

 spht off and it is then clearly to be seen (Plate 16, figs. 20, 21) that the limits 

 between the outermost and the next silica-layers are perfectly smooth. From 

 this it follows that the spines are not formed until after the spicule has attained 



