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 /i. 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 fi. The constancy of the number (seven) 

 of these terminal spines seems very remarkable, since this number is apparently 

 in no way connected eitlier with the triaxon (hexactine) ground plan of all hexac- 

 tinellid spicules, or the physical (crystallograpliic) 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 fi 

 in total diameter, and have main-rays 5-8 /z long and 2.7-.5 yu thick. Each 

 main-ray usually bears seven or eight end-rays 36-62 /i in length. These 

 measure in thickness 1.5-3 ju at the base, and 0.5-1.2 n at the thinnest point near 

 the end, and 1-1.5 /x at the end itself. The terminal spine- verticils measure 6- 

 11 /i in transverse diameter. 



The plumicomes (Plate 12, figs. 21-23) have a central thickening about 

 3.5 M 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 n 

 thick. Near their end they are thickened to an oval knob, 2-3 fi in transverse 

 diameter, from which the end-rays arise. A terminal cylindrical rod, 0.8-1.4 /x 

 thick, 2-4 fi long, and rounded 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 ii. 

 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 fj. 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 ^ in total diameter. Their main-rays, which are 

 regularly arranged and enclose angles of 90° with their neighbours, are 5-11 n 

 long and 3-7 ix 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 fi long, 3-4 ^ thick at the base, and about 2 ;u at the end. The 

 ends of many of them are divided into short and stout, irregularly bent, trans- 



