THE SPONGES OF THE WEST-CENTRAL PACIFIC 



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Text Figure No. 12. Portion of the skeletal network of Ircinia halmiformis, X 182. 



shall Islands (his specimens C37A and C101) and at least one specimen 

 from Eniwetok Atoll in the Marshall Islands (his specimen Zl). 



These specimens from the Marshall Islands may be described as con- 

 sisting each of a basal sheet, 3 to 5 mm thick and often as much as 4 cm 

 square. On this, ridges 7 mm high and 2 to 3 mm thick arise. These ridges 

 are arranged in a highly complicated or labyrinthine manner. The deep 

 valleys between them are only 1 to 3 mm wide. 



When preserved in alcohol, the color is drab. The consistency is spongy, 

 but it is easily cut, a remarkable factor when compared to other species in 

 the genus Ircinia. 



The surface is microconulose but very complicated. The pores are 

 closed, but oscules appear in considerable numbers on the surfaces of the 

 labyrinthine ridges. They are usually much less than 1 mm in diameter, 

 often only 2 to 7 mm apart. 



The ectosome is a fleshy dermis, about 20 /x thick. The endosome is a 

 fibro-reticulation and contains numerous typical Ircinia filaments. 



The skeleton, as already noted, contains filaments, in this case 2 to 3 /x, 

 in diameter. The fibers contain rather large foreign material, sand grains 

 often as much as 50 /x in diameter. The total fiber diameter ranges from 30 to 

 80 ft. Where it is arranged in ascending fascicles, the latter are often about 

 200 ix in diameter. 



This unique species was first described as Hircinia halmiformis by Len- 

 denfeld, 1888, page 183, from the Australian region. The agreement of 

 the Marshall Island specimens with those of Lendenfeld is astonishingly 

 close. 



