200 THE SPONGES OF THE WEST-CENTRAL PACIFIC 



The depth was 2 meters, and the substrate was dead coral. 

 U.S.N.M. No. 22935, My No. M. 305, collected June 11, 1949, by hand 

 while wading in the south portion of the lagoon at Ailing-lap-lap Atoll. 

 The depth was 30 mm, and the substrate was dead coral. 



Text Figure No. 135. Spicules of 

 Spirastrella decumbens. A: Tylostyle, 



*HL X 182. B: Spiraster of the larger size 



range, X 782. C : Spiraster of the small- 



O cr size range, X 782. 



This species also was collected by T. E. Bullock at Eniwetok Atoll in the 

 summer of 1948 and is represented by his Specimen No. Z 106. 



This species is incrusting, from 1 to 3 mm thick, spreading laterally 

 indefinitely, often as much as 10 cm. 



The color in life is typically brown, varying from flesh color to chocolate 

 and occasionally to red. The consistency is spongy. 



The surface is level and shows river systems to a small extent, but not as 

 conspicuously as in the preceding species. As in potamophera, however, the 

 oscules, which are closed in all collected specimens, were probably at the 

 mouths of the river systems. The pores are about 100 jx in diameter and 

 plentifully scattered in the regions between the evident subdermal canals. 



The ectosome is represented by a very thin fleshy dermis, which, as in 

 the preceding species, contains numerous microscleres. The endosome is 

 represented by a rather confused structure, chiefly protoplasmic. 



The skeleton consists of tylostyles with elongate heads, typically half 

 again as long in the long axis of the spicule as the greatest diameter of the 

 heads. These are considerably smaller than in potamophera, ranging up, 

 however, to as much as 6 fx by 380 jx. The microscleres also are rather sharply 

 divided into two categories. Those of the larger category are only 36 /x long, 

 often less ; and those of the smaller category are often only 6 /.<. long. 



At Ebon Atoll and Ailing-lap-lap Atoll, this species occurred in the 

 same ecological placement as the preceding one. Therefore, it does not seem 

 likely that the differences are due to environmental circumstances. Ridley, 

 1884, page 470, described Spirastrella decumbens from the East Indies. His 

 description omits some of the details here given, but details that are available 

 match closely those of the species here identified as decumbens. As noted, 

 this differs from potamophera in having smaller megascleres and smaller 

 microscleres of both size ranges. Also, it has a greater tendency to be brown- 

 ish, although the red pigment also is obviously present. It is here suggested 

 that there are only four species in the genus Spirastrella, as now embodied in 

 the literature. These are cunctatrix, coccinca, decumbens, and potamophera. 

 All four are characterized by persistently incrusting shape. The many other 



