HYALONEMA (OONEMA) CRASSIPINULUM. 335 
The dermal superficial pinules have distal rays 250-790 u 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 u long, most frequently 600-650 yu. It is 15-24 pu 
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 u. The lateral rays are cylindroconical, and 45-95 pu 
long. They bear small, sparse, broad, and low, conical spines. 
The small 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 u, basal thickness 10-17 4, maximum thickness together 
with the spines 28-65 y; lateral rays, length 45-70 up. 
The canalar pinules (Plate 92, figs. 16, 17) are pentactine or hexactine. 
The distal ray is straight, 120-150 uw long, and 5-9 uw thick at the base. It is 
slightly thickened above, gradually attenuated to a fine point, and bears rather 
sparse, small, straight spines directed obliquely upwards. Its maximum thick- 
ness, together with the spines, is 7-30 uw. The lateral rays are 45-95 uv long; the 
proximal, when present, is 50-70 u. Both the lateral rays and the proximal 
are spiny. 
There seems to be no great difference between the hypodermal and hypo- 
gastral pentactines. Both have straight, conical, blunt rays. The lateral 
rays are 230-550 u» long; the proximal ray is 400-700 » long and 15-60 y» 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 25-80 u. 
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 w thick. 
The central tyle is 10-34 » in diameter, that is 2—5 » more than the adjacent 
parts of the spicule. 
