>* 



I 





i 









THE SPONGES. 



47 



distal ray. The proximal ray* is ordinarily longer than the tangentials, but 

 occasionally is very short, especially in the case of pentacts lying over the 

 main canals. The proximal ray is roughened with sharp microtubercles in 

 its upper part. The tangential rays commonly show a few sharp micro- 

 tubercles near the point of intersection, but may be smooth, or on the 

 other hand extensively covered with microtubercles in this region. The 

 tangential rays are straight or very slightly incurved ; exceptionally some- 

 what outcurved. The spicules vary in size in the same individual, the 

 tangential rays measuring 400-750 /x x 36-48 /x, the proximal ray measur- 



ing commonly 780-1000 /x x 50-60 /x. 



The tangential rays of the pentacts overlap and give rise to a mesh- 

 work, the meshes of which are very commonly square or squarish. The 

 size of the mesh varies considerably in different regions of the same indi- 

 vidual as well as in different individuals; diameter commonly 340-680 /x. 

 Where the pentacts are crowded, some lie at a slightly lower level than 

 others, and so interfere with the regularity of the meshwork. 



On the upper part of the stalk a few of the hypodermal pentacts 

 remain. Some are like those of the body ; others differ in that they are 



quite smooth. 



The spinose microsclere (Figs. 1, 4, 5, 9, Plate 5) found in all the 



species of the genus is here present in the greatest abundance, everywhere 

 filling the parenchyma. While the true discohexact, in which none of 

 the rays are branched, occurs in all of the specimens, and in a few is the 

 predominant form, it is in most of the specimens uncommon. The rays 

 of the discohexact are 80-110 /x x 8 /x, tapering strongly toward the apex, 

 which is capped by a watchglass-shaped end-plate, 10-12 /x in diameter, 

 divided marginally into about 6 strong teeth. The rays except near the 

 centre of the spicule bear strong recurving spines, which diminish in size 

 toward the apex of the ray. 



In most of the specimens the great majority of these spicules are im- 

 perfect hexasters (Figs. 1 and 4, Plate 5). Spicules in which 3 or 4 of 

 the original hexact rays are branched, while the others remain single, are 

 the commonest types, although perfect hexasters, in which all 6 original 

 rays are branched, occur. In the hexasters, imperfect or perfect, the 

 principal rays are smooth and short, and the combined length of princi- 

 pal and terminal equals the length of the undivided hexact ray. The 

 terminals are spinose and capped, as in the true hexact forms. The 



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