HYALONEMA (OONEMA) CRASSIPINULUM. 
335 
The dermal superficial pinules have distal rays 250-790 n long. Their 
length frequency-curve exhibits, like that of the gastrals, two very distinct 
elevations, so that also among these pinules two kinds, a large and a small one, 
must be distinguished. 
The large dermal pinules (Plate 92 , fig. 6) are pentactine. Their distal ray 
is usually straight and 500-790 /x long, most frequently 600-650 /x- It is 15-24 /x 
thick at the base, and thickened above. At its point of maximum thickness, 
which lies a little above the middle, it attains a transverse diameter about twice 
as great as its basal thickness. The distal ray ends with a low and broad termi- 
nal cone. Its spinulation is similar to that of the gastral pinules. The spines 
are proportionately smaller. The maximum diameter of the distal ray, together 
with the spines, is 50-90 /x. The lateral rays are cylindroconical, and 45-95 n 
long. They bear small, sparse, broad, and low, conical spines. 
The synall dermal pinules (Plate 92 , figs. 7, 18) are rather similar to the 
larger ones and, like them, all pentactine. Their dimensions are: — distal 
ray, length 250-440 /x, basal thickness 10-17 /x, maximum thickness together 
with the spines 28-65 /x; lateral rays, length 45-70 n- 
The canalar pinules (Plate 92 , figs. 16, 17) are pentactine or hexactine. 
The distal ray is straight, 120-150 /x long, and 5-9 n thick at the base. It is 
slightly thickened above, gradually attenuated to a line point, and bears rather 
sparse, small, straight spines directed obliquely upwards. Its maximum thick- 
ness, together with the spines, is 7-30 /x. The lateral rays are 45-95 tx long; the 
proximal, when present, is 50-70 /x. Both the lateral rays and the proximal 
are spiny. 
There seems to be no great difference between the hypodermal and hypo- 
gaslral pentactines. Both have straight, conical, blunt rays. The lateral 
rays are 230-550 /x long; the proximal ray is 400-700 /x long and 15-60 /x thick 
at the base. 
The hexactine megascleres generally have fairly equal rays. In some, two 
opposite rays are a little longer than the others, but the difference never appears 
to be great. The hexactine megascleres observed are 0.8-1. 2 mm. in diameter. 
The basal thickness of their rays is 25-30 m- 
The amphioxes of the dermal and gastral membranes (pore-sieve reticula- 
tions) and the choanosome are centrotyle, straight or curved, sometimes very 
considerably, and 0.7-1. 7 mm. long. Near the middle they are 8-29 ^ thick. 
The central tyle is 10-34 /x in diameter, that is 2-5 ^ more than the adjacent 
parts of the spicule. 
