THE SPONGES OF THE WEST-CENTRAL PACIFIC 



249 



Text Figure No. 172. Spic- 

 ules of Plakinolopha mira- 

 bilis. A: Strongyle, X 182. 

 B and C: Modified cal- 

 throps, X 782. D: Micro- 

 spined rods, X 782. 



The ectosome is distinctive both as to structure and color. It is at least 

 100 jx thick and is crowded with spicules in confusion. The endosome contains 

 some tracts of spicules. These tracts are about 100 /x in diameter and contain 

 30 to 50 spicules per cross section. 



The skeleton comprises, first of all, long smooth strongyles 7 \x by 400 fi 

 in dimensions. These crown the tracts and are scattered in the ectosome. A 

 few also occur loose in the endosome. As megascleres, there are also fairly 

 numerous spicules which might be called lophotetractines. These are small 

 tetracts of the calthrops type, smooth except near the end, where a small 

 number of very large spines occur. The rays of these spicules are about 25 /x 

 by 80 jx. There are also microscleres which are straight spined rhabds, 2 /x 

 thick and 12 \x long. 



This species is so very distinctive that there are good grounds for argu- 

 ing that a new genus should be erected for it. Placinolopha was established by 

 Topsent 1897, page 429, for the species bedoti. This has oxeas up to 7 /x by 

 160 fx only, but the spicules with spiny ends are much larger than in mirabilis. 

 Furthermore, many of these are not spiny on all four terminations but on 

 only two or three of their terminations; and, in fact, there are triacts and 

 tetracts present which are not spiny at all. There are none of the small 

 microscleres. The second species in the genus Placinolopha is spinosa Kirk- 

 patrick, 1900, page 350. This has no diactinal microscleres at all. Both bedoti 

 and spinosa are from the East Indian region. 



The name mirabilis is selected from a Latin word meaning "amazing." 



FAMILY CHONDRILLIDAE Gray 



GENUS CHONDRILLA Schmidt 



Chondrilla australiensis Carter 



Text Figure No. 173 



This species is here represented by the following : 

 U.S.N.M. No. 22956, My No. M. 330, collected June 28, 1949, by diver near 

 the north side of the lagoon near the old coast guard radio station at 



