STAUROCALYPTUS HAMATUS. 115 



indentures are not restricted to the outer surface but affect the whole of its 

 superficial, clearly stratified part, down to the more homogeneous central part, 

 the surface of which also shows the indentures. 



The hypodermal pentadines (Plate 18, figs. 8-10) have a straight or slightly 

 curved proximal ray, which is 0.5-2.2 mm. long and 9-22 n thick at the base. 

 The lateral rays are vertical to the proximal ray and in the same spicule often 

 unequal, the longest being 120-210 fi, the shortest 80-170 fx long. All these rays 

 are blunt. The tips of the lateral rays are spiny. 



A triactine with one longer and two shorter rays, opposite in the same straight 

 line (axis), which enclosed an angle of 70° with the axis of the long ray was 

 observed in the spicule-preparations. The long ray of this spicule was 860 m 

 long, the two short rays were 260 and 280 fi. The distal parts of all the rays 

 were spined. 



The dermal spicules (Plate 16, figs. 40^3) are usually simple, straight or 

 slightly curved, diactine rhabds (Plate 16, figs. 42, 43), 335-470 n long, and 7- 

 13 M thick at the thickest point, which is usually situated near the middle. An 

 axial cross can usually be discerned at or near the middle. The two rays are 

 cyhndroconic and terminally rounded. Their ends are usually a half to a third 

 as thick as the thickest portion of the middle-part of the spicule. Sometimes, 

 however, they are thinner than that, down to a quarter of the maximum thick- 

 ness of the middle, or thicker, up to nine tenths of this, or even slightly more. 

 The two ends of the same spicule are usually somewhat unequal, one being 1 ii 

 or so thicker than the other. The whole spicule is covered with conic, vertically 

 arising spines, 0.5-2 n long. The spines are more numerous at the ends than in 

 the middle. This difference in the degree of spinulation of the different parts is 

 the more clearly pronounced the longer the spicule is. 



Besides these simple diactine dermal rhabds similar ones with a tyle, situated 

 either more or less centrally or, rarely, terminally, are met with. The tj^le may 

 be a simple thickening, and concentric with the axis of the spicule, or it may be 

 one sided (Plate 16, fig. 41), or composed of two protuberances (Plate 16, fig. 40). 

 These protuberances, which are obviously ray-rudiments, are up to 10 yu long and 

 covered with spines like the other parts of the spicule. 



I found in the spicule-preparations a few tetractines (stauractines) and 

 angularly bent diactines with rays similar in regard to their spinulation to those 

 of the rhabds above described. The former have rather unequal rays 160-230 n 

 long and 9-10 ix thick at the base. One of the latter had rays 48 /n long, 8 m 

 thick at the base, and 5 ix at the end. 



The oxyhexasters, hemioxyhexasters, and oxyhexactines with straight rays 



