40 HOLASCELLA ANCORATA. 
The smaller, spined hexactine and tetractine megascleres (Plate 24, figs. 1, 2) 
are 1-4 mm. in maximum diameter. Their rays are unequal, often curved, 
up to 1.7 mm. long, 12-17 u thick at the base, and rounded at the end or blunt- 
pointed. The bases and often also the tips of the rays are smooth, the other 
parts show sparse, broad, sharp-pointed spines. 
The comital spicules (Plate 24, fig. 9) are di- to tetractine. Their rays are 
straight or irregularly curved, gradually attenuated distally, and terminally 
rounded. The end-part is usually somewhat thickened and spined. The other 
parts of the spicule are smooth. The rays attain a very considerable length. 
Measurements of this dimension cannot, however, be given since all the long 
rays observed were broken off. The longest intact ones seen were 1.5 mm. long. 
The rays are 8-28 » thick at the base and attenuated distally to 5-8 yu. The 
spined end-part is 7-10 » thick. In the tetractine and triactine comitals two 
opposite longitudinal rays lie in a straight line and are longer than the transverse 
ones (one). In the triactine forms the centre is markedly thickened on the side 
opposite the single transverse ray (Plate 24, fig. 9). The diactine forms are cen- 
trotyle. The central tyle measures 14-36 » in diameter. The proportion of the 
basal thickness of the rays to the transverse diameter of the tyle is 1: 1.4 to 1: 3, 
usually about 1:1.6. The two rays of these spicules are usually unequal in 
length and sometimes one of them is reduced to a mere knob. Such excessive 
longitudinal reduction is always associated with a considerable thickening. 
' In an extreme form of this kind one ray was observed to be over 2 mm., the 
other only 44 uw, long. The central tyle measures 40 u in diameter; the long ray 
is 16 » thick and nearly cylindrical. The short ray is 33 » thick at the base and 
farther on it is 44 « thick. This knob-like rudimentary ray is covered with small 
spines down to within a short distance of its base. 
The proximal and lateral rays of the hypodermal and hypogastral hexactines 
(Plate 23, figs. 12, 13) are 5-9» thick at the base. They are cylindrical or 
slightly attenuated distally, and usually rounded at the end, rarely pointed. 
Their tips are generally spined, their other parts smooth. The proximal ray 
is 0.9-1.5 mm. long, the lateral rays 370-450 ». The distal ray is 220-450 u 
long, at the base as thick or somewhat thinner than the other rays, and distally 
thickened. At its thickest point, which lies near the distal end, it measures 
17-40 w in diameter. The proximal part and the extreme tip are smooth, the 
other parts of it more or less spined. The spines increase in size and number 
* distally. They arise very obliquely and point towards the tip of the ray. The 
hypodermals are similar to the hypogastrals. Hexactines with thick strongly 
