HYALONEMA (PHIALONEMA) PATERIFERUM. 
367 
spines on their proximal ray. Wilson ( loc . cit .) gives the length of one of these 
spicules (of form A or B ) as 700 n, and the thickness of its tyle as 12 fi. The 
diactine pinules of the forms examined by me are shorter, not more than 470 n 
long. In form D, where I found the largest number of them, the distal ray is 
140-200 /d long, 4-5 n thick at the base, conic, and attenuated distally to a very 
slender terminal cone. This terminal cone and a small region at the base of 
the ray are free from spines; the remaining parts bear small spines strongly 
inclined towards the tip of the ray. The proximal ray in the diactine pinules 
of this form (D) is 80-125 fx long. The tyle, which consists of four knob-like 
protuberances (the rudiments of the four reduced lateral rays), measures 9-17 /j. 
in transverse diameter. A diactine pinule of form C, which I measured, had a 
distal ray 350 n long, and 5 n thick at the base, a proximal ray 120 n long, and a 
central tyle 15 m in transverse diameter. 
The lateral rays of the ( hypodermal and hypogastral ) pentactines are, accord- 
ing to Wilson (loc. cit.), in the forms A and B 150-600 n long, and 12-48 n thick 
at the base. In form D, where alone I could measure a large number of these 
spicules, their lateral rays are 120-360 m long and 12-30 n thick. The proximal 
ray is generally longer than the lateral rays. The lateral rays are straight, 
smooth, and pointed; the proximal ray is similar, or, rarely, reduced in length, 
and thickened and rounded at the end. 
The hexactine megascleres. Wilson (loc. cit.) gives the measurements of one 
of these spicules (of form A or B) thus: — length of rays 700 n, basal thickness 
48 id. In form D these hexactines have rays 25-41 n thick at the base. One 
of the intact ones of this form was 1.2 mm. in diameter. 
The choanosomal rhabds are usually centrotyle amphioxes. In the forms A 
and B they measure, according to Wilson (loc. cit.), 0.5-3 mm. by 8-28 n. In the 
forms examined by me they appear to be similar. 
The paratangential superficial and the radial subdermal and subgastral 
centrotyle amphioxes are in form D 320-520 m long and, near the middle, 3-10 n 
thick. The central tyle is 11-13 n in diameter. 
The stalk-spicules are in form A, where alone they have been observed, 
according to Wilson (loc. cit.), 0.13-1 mm. thick, attenuated below, and pro- 
vided with “the well-known annular ridges.” 
The acanthophores (Plate 52 , figs. 17-19) are, according to Wilson (loc. cit.), 
in form A di- to hexactines, tetractines with unequal rays being most frequent. 
The measurements given by him are 900 n for the length of a diactine, and 250 n 
for the length of a ray of a tetractine. In form F I found di- to pentactine 
