FARREA OCCA SCUTELLA. 
123 
planes, passing through the axis to which these forks belong and either of the 
two other axes of the spicule. The end-ray forks of opposite main-rays do not 
lie in the same plane. As far as I could make out the planes of such forks are 
opposite, and usually symmetrical, in such manner that the angle enclosed by 
them with either of the two axial planes above mentioned are supplementary; 
added together they give 180°. When there are three or four end-rays the most 
divergent usually enclose an angle of about 90°. 
The clavules with large teeth (Plate 27 , figs. 1-5, 6b, 7-11, 13-17) are gener- 
ally 300-370 n long; a few are shorter, down to 210 ^ in length. They consist 
of a centrum, from the lower end of which there arises a shaft, and from the 
opposite, upper end of which arises a verticil of recurved teeth. The centrum is a 
short cylinder, 6.5-12.5 usually 9-12 /x, in transverse diameter, which generally 
bears one or a few spines at its lower end. These spines are oblique, inclined 
towards the shaft, and 0.5-2. 3 m long. Their size seems to be in inverse propor- 
tion to their number; the solitary ones are the largest. At the base, where it 
arises from the centrum, the shaft is 4-8 m thick; its basal part is conic; farther 
on it becomes nearly cylindrical; just before the end it is 2. 5-4. 5 m thick. The 
end is abruptly and bluntly pointed and frequently slightly thickened. The 
proximal and middle-parts of the shaft bear oblique spines, inclined towards 
its end. These spines are similar to those on the centrum, but smaller. The 
end-part bears stouter, vertical spines, 0.6-1. 5 n long. The number of these 
spines is variable. Their size appears to be in inverse proportion to their num- 
ber. A smooth belt sometimes intervenes between the middle region with 
oblique, and the terminal region with vertical spines. There are usually nine, 
more rarely ten, recurved teeth which form the verticil at the upper, distal end 
of the centrum. They are fairly equal in the same spicule, and regularly ar- 
ranged, the angle between adjacent ones being the same. The verticils formed 
by these teeth measure 39-53 m in transverse diameter. The individual teeth 
are conic, 5-7 m thick at the base, and uniformly attenuated towards the sharp- 
pointed end. They are uniformly curved, concave to the centrum, and their 
chords usually enclose angles of 55°-63° with the axis of the centrum and shaft. 
The teeth generally bear spines, sometimes 0.7 m long, some distance below their 
ends. These spines are confined to a median line following the outer, convex 
side of the teeth. Usually they form short saw-like rows on the upper margin. 
Sometimes they are very conspicuous (Plate 27 , figs. 13, 14), sometimes so small 
as to be hardly visible (Plate 27 , figs. 16, 17). The apex of the tooth- verticil is 
generally smooth and dome-like (Plate 27 , figs. 1-5, 6a, 7, 8, 11, 13, 14, 16, 17). 
