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 clamles with large teeth (Plate 27, figs. 1-5, 6b, 7-11, 13-17) are gener- 

 ally 300-370 M 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 m, usually 9-12 n, 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, incUned 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 ^ 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 

 obhque, 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 indi\'idual teeth 

 are conic, 5-7 n 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 fx. 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-Uke (Plate 27, figs. 1-5, 6a, 7, 8, 11, 13, 14, 16, 17). 



