110 LANUGONYCHIA FLABELLUM. 
The distal part of the end-rays, beyond the thinnest point, is smooth. At the 
end each end-ray bears a verticil of seven large anchor-teeth, like recurved spines 
with a maximum length of 11 ». The basal parts of these terminal spines 
coalesce to form a kind of convex terminal disc. The transverse diameter of 
these terminal spine-verticils is 12-16 ». The constancy of the number (seven) 
of these terminal spines seems very remarkable, since this number is apparently 
in no way connected either with the triaxon (hexactine) ground plan of all hexac- 
tinellid spicules, or the physical (crystallographic) properties of the silica of 
which they consist. 
The small discohexasters differ from the large ones described above only in 
regard to their size and the number of their end-rays. They measure 82-140 u 
in total diameter, and have main-rays 5-8 uw long and 2.7—5 y» thick. Each 
main-ray usually bears seven or eight end-rays 36-62 uw in length. These 
measure in thickness 1.5-3 w at the base, and 0.5-1.2 » at the thinnest point near 
the end, and 1-1.5 yu at the end itself. The terminal spine-verticils measure 6- 
11 yu in transverse diameter. 
The plumicomes (Plate 12, figs. 21-23) have a central thickening about 
3.5 « in diameter and regularly arranged main-rays, enclosing angles of 90° with 
their neighbours. The proximal part of the main-rays is cylindrical, and 1-1.5 » 
thick. Near their end they are thickened to an oval knob, 2-3 yu in transverse 
diameter, from which the end-rays arise. A terminal cylindrical rod, 0.8-1.4 u 
thick, 2-4 » long, and reunded at the end, arises from each knob. This rod, 
which lies in line with the proximal part of the main-ray, appears as its termina- 
tion. The total length of the main-rays (including the terminal rod) is 10-14 u. 
The end-rays, of which there may be about twenty on each main-ray, are curved. 
in an S-shaped manner, and are 30—40 uy long. 
The irregular discohexasters with primary and secondary end-rays (Plate 12, 
fig. 20) are very rare. I found only three. These spicules may be malformed 
discohexasters. Since, however, the three observed are very much alike and 
since no intermediate forms connect them with the other hexaster-forms, they 
may also be spicules sui generis. 
They measure 120-140 u» in total diameter. Their main-rays, which are 
regularly arranged and enclose angles of 90° with their neighbours, are 5-11 yu 
long and 3-7 w thick. Each main-ray bears two or three basally curved, but for 
the greater part of their length fairly straight, strongly spined, primary end-rays. 
These are 50-60 » long, 3-4 u thick at the base, and about 2 » at the end. The 
ends of many of them are divided into short and stout, irregularly bent, trans- 
