HYALONEMA (OONEMA) SEQUOIA. 
351 
somewhere near the tip, an umbilicus-like 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 asymmetrical 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 m 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 never 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 m 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 ^ thick at the base. But smaller forms with correspond- 
ingly thinner rays also occur. 
The hypodermal and hypogastral pentactines have a straight, cylindroconical, 
terminally rounded proximal ray, usually 0.5-1. 2 mm. long, ancl 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. 
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 ^ 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 n more than the adjacent parts of the 
spicule. 
