BATHYDORUS LAEVIS SPINOSISSIMUS. 
97 
rounded or, rarely, sharp-pointed (Plate 14 , fig. 2), or first thickened and then 
attenuated to a blunt point (Plate 14 , fig. 4). The ends of the normal rhabds, 
with rays not differing very much in length, are 3-45 n thick, which is a sixth to 
three quarters, sometimes nearly quite as thick as their middle-part. The small 
rhabds are on the whole less attenuated towards their ends than the large ones. 
The two rays composing the rhabds usually differ more or less in respect to 
the shape and thickness of their ends, and also in respect to their length. One 
end is often much more blunt than the other, and the difference in the thickness 
of the two ends is sometimes so great that one end is more than twice as stout 
as the other. The difference of the two rays in length is usually inconsiderable ; 
occasionally, however, one ray is reduced very considerably in length, and then 
this difference is great. In four rhabds of this kind one (the normal ray) meas- 
ured over 2 mm. long, the other (the reduced ray) only 100-290 n. These 
greatly shortened rays are terminally thickened either gradually or abruptly, 
in which latter case their end appears as a terminal tyle, the transverse diameter 
of which may be nearly twice as great as that of the base. 
In some of the large rhabds, particularly the large prostals, one or more 
thickenings are observed some distance below the end (Plate 14 , figs. 7-9). 
Occasionally such thickenings also occur near the centre of the spicule. 
The end-parts of all the small and most of the large rhabds for a distance of 
about 80-100 n are covered with vertically arising spines 1-2 n high (Plate 14 , 
figs. 1-4, 8-10). Some of the largest rhabds appear to have smooth end-parts 
(Plate 14 , fig. 7). Apart from their end-parts the rhabds are perfectly smooth. 
On the end-parts of some rhabds the spines are more numerous than on the end- 
parts of others. Also in this respect the two rays of the same rhabd often differ. 
The ends of the rays reduced in length are always densely spined. 
Two kinds of angularly bent diactines (Plate 16 , fig. 19) can be distin- 
guished, one with an obtuse angle between the two rhabd-rays, the other with 
an angle of 90° or less. The former are similar to the rhabds described above, 
from which they differ by the angle between the rays being only about 
120° instead of 180°. I consider these diactines as derivates of the ordinary 
rhabds. In the latter the angle between the two rays is usually 75°-90°. The 
rays of these spicules are 0.3-1. 5 mm. long, 7-20 n thick at the base, straight, and 
rather unequal in length. At the point of junction of the two rays the spicule is 
thickened to a conspicuous tyle. I have not observed any angularly bent diac- 
tines with angles of 90°-120° which might be considered as transitions between 
the two kinds of these spicules observed, and I am not sure whether the forms 
