HYALONEMA (OONEMA) SEQUOIA. 351 



somewhere near the tip, an umbiUcus-hke spot around which they are disposed 

 quite irregularly (Plate 87, figs. 4-7). Very frequently a difference in the posi- 

 tion of the spines on opposite sides is observed in the distal part of the ray, 

 which renders it asj'mmetrical in appearance (Plate 87, fig. 3a; Plate 88, fig. 13a). 

 These irregularities are so frequent that they can hardly be considered as 

 abnormities. In some places the spines are isolated and irregularly scattered; 

 in others they are arranged in spiral rows and appear to rise from the crests of 

 scale-like protuberances of the central solid part of the ray. 



The lateral rays are conical, blunt, at the base slightly thinner than the 

 distal ray, and 33-195 n long; they are usually one tenth to one third of the dis- 

 tal ray in length. In the smaller pinules they are on the whole relatively much 

 longer than in the larger ones. In the latter I have ne\'er found them more 

 than a seventh of the distal ray in length. In the large pinules the lateral rays 

 are spined more or less densely throughout their whole length. Their spines 

 are vertical, and similar in shape and size to those on the basal part of the distal 

 ray (Plate 87, fig. 3b; Plate 88, figs. 12b, 13b). The lateral rays of the smaller 

 pinules are spined only in their distal part, and their spines are very small. 



The proximal ray of the rare hexactine superficial pinules is similar in 

 shape and size to the laterals. The proximal rays measured are 57-95 // long. 



The hexactine megascleres (Plate 85, figs. 20, 21) have smooth, usually 

 somewhat curved, rarely angularly bent, cylindroconical, terminally rounded 

 rays. In the smaller forms the six rays are usually fairly equal in size, in the 

 larger two opposite rays are generally considerably longer than the other four. 

 The hexactine megascleres are usually 0.5-5.5 mm. in maximum diameter, and 

 their rays are 20-140 /u thick at the base. But smaller forms with correspond- 

 ingly thinner rays also occur. 



The hypodermal and hypogastral pentadines have a straight, cylindroconical, 

 terminally rounded proximal ray, usuallj' 0.5-1.2 mm. long, and 20-40 n thick 

 at the base. The lateral rays are much shorter, usually only 0.3-0.6 mm. long. 



The amphioxes are of three kinds: — 1, small and slender, 2, small and stout, 

 and 3, large. i 



The small and slender amphioxes (Plate 89, fig. 15a), which predominate in 

 the interior, are centrotyle, straight or curved, sometimes very considerably 

 bent, usually 0.6-2 mm. long, and 6-20 yu thick near the middle. The pro- 

 portion of length to thickness, is in these spicules 1000 : 7 to 1000 : 13. The 

 central tyle is 10-21 ^ thick, that is 1-4 /x more than the adjacent parts of the 

 spicule. 



