HYALONEMA (OONEMA) BIANCHORATUM PINULINA. 315 



also somewhat hour-glass-shaped, and is at its thinnest point 9-17 n thick. 

 Its spines are usually quite strongly divergent, and markedly curved, concave 

 towards the ray. They attain their greatest size one half to two thirds of the 

 length of the distal ray from the centrum, or still higher up, and here the distal 

 ray, together with the spines, attains a maximum thickness of 30-65 m- The 

 lateral rays are similar to those of the pinules of the upper part of the sponge, 

 above described, but stouter and provided with larger spines. They attain a 

 length of 35-80 n. Of hexactine forms I found (and measured) only two, with 

 proximal rays 12 and 20 ^ long respectively. One of these is conical and pointed, 

 the other (Plate 82, fig. 26) cylindrical and terminally rounded. 



The hypodermal pentadines (Plate 83, figs. 65-67) have very blunt, conical 

 rays. The proximal ray is often somewhat curved ; the lateral rays are usually 

 straight, occasionally curved in the plane, vertical to the proximal, in which they 

 lie. The proximal ray is 0.4-1.3 mm. long, and 15-70 yu thick at the base. The 

 lateral rays are 260-610 yu long. Those of the same spicule are usually fairly equal, 

 more rarely conspicuously unequal. In a hypodermal pentactine with particu- 

 larly unequal laterals the longest is 610 yu in length, the shortest only 390 fx. 



The hypogastral pentadines (Plate 83, fig. 68) are similar to the hypodermal, 

 but much smaller. Their proximal ray is 210-800 ^ long, and 12-46 ix thick 

 at the base. Their lateral rays are 150-460 fi long. 



The hexadine megasderes (Plate 83, figs. 63, 64) are 0.35-5.5 mm. in maxi- 

 mum diameter. Their rays are straight or sUghtly and irregularly curved, 

 7-120 IX thick at the base, attenuated distally, at first more gradually, then more 

 rapidly, and pointed at the end. In all the larger and in many of the smaller 

 ones two opposite rays are considerably longer than the other four. Some of 

 these spicules are nearly twice as long as broad. 



The dermal, gastral, and choanosomal amphioxes are straight or more or less 

 curved, rarely angularly bent, centrotyle, 0.5-2.8 mm. long, and 7-59 ^ thick 

 near the tyle. The tyle is 9-60 ^ in.diameter, that is 1-23 y., usually 2-6 yu, more 

 than the adjacent parts of the spicule. The dimensions of the different kinds 

 of these spicules (dermal, gastral, and choanosomal) in the two specimens are 

 given in the table on page 314. 



The amphioxes of the dermal and gastral membranes are in both specimens 

 considerably shorter, stouter, and less curved than those of the choanosomal. 

 The gastrals are in both specimens stouter than the dermals. The amphioxes 

 of specimen h are on the whole slightly stouter than those of a. This difference 

 is particularly well-pronounced in the gastrals. The two limbs of the angularly 



