11 
you can see how much the type varies. Nearly always the 
„manubrium” is greater than the „dentes’”’, more or less lexuous 
and ending blunt (fig. 1). The angle that I have named & is 
generally little more than 90° (fig. 1); in fig. 21 ® is much larger 
but these spicules are very rare. The relation between d and 
d’ is also varying. In figg. 3 and 21 d is much longer than d', 
in fig. 4 on the contrary d’ is longer than d. I have seen speci- 
mens where d' was eighteen times longer than d. The ends of 
d' are are either sharp pointed as in the figg. 4 and 21, or 
blunt as in the figg. 1, 2 and 3. 
4°. M. ta @ > 90° [„attenuato-expando-ternate”]. This form is not very 
common; often totally absent. The form is varying rather much. 
The „dentes” are straight or flexuous, sharp pointed or blunt, 
long and slender or short and stout. Two blunt ones are to be 
seen on Plate II. figg. 6 and 7. The manubrium is generally 
long. 
5°. M.ta.0 < 90° [„recurvo-ternate”’] always very frequent. They 
appear especially in the roots, and, having the teeth beneath, 
they do the function of anchors by fixing the root in the sand. 
They have the same size as the „attennato-expando-ternate’” spi- 
cules; both are much smaller than the bifurcated ones. The 
teeth are always sharp-pointed, but varying in length, The 
figg. 8, 9, 10 and 11 show different kinds of them. 
6, M.ta. Between M.ta. ® > 90° and M. ta. © < 90° there are many 
connections. When the angle ® is nearly or wholly right, Ihave 
put in the formula: &® = 90°. Thus when the angle is for in- 
siance 100° or even more, you can either write ® = 90° or omit 
the whole indication (M. ta.). All ‘these forms Bowerbank na- 
med „patento-ternate.” Even when the angle is not quite 90°, 
it often makes the impression of it. In every case this is quite 
different from the true M.ta.® < 90° or M.ta.9 > 90°. In the 
Thenea muricata Gray there are plenty of spieules of this kind; the 
angle® varying from 90°—110° (120°). It is not impossible that all 
these M.ta. are rudimentary bifurcated spieules. I will call to 
mind that the teeth d’ often are extremely small. The manu- 
