THE SPONGES OF THE WEST-CENTRAL PACIFIC 113 



latter size, however ; most of them are less than 6 mm in diameter. The walls 

 of these chimneys are less than 1 mm thick. The central portion, however, 

 is not completely hollow but is partially subdivided by fibers which outline an 

 exceedingly openwork and cavernous endosome. 



The color in life was dark olive and medium yellow; the large chimney 

 was medium yellow ; the other chimneys were between dark olive and yellow. 

 The consistency was stiffly spongy, rather fragile. The dried specimen first 

 became a pale dull red, but after six months it became brown. The dried 

 specimen is very brittle. 



The surface is exceptionally smooth. The pores are very small, and the 

 situation with regard to oscules is very difficult to understand. There is one 

 obvious oscule at the summit of the single largest chimney; it is 8 mm in di- 

 ameter. All the other upright projections are closed over at the upper end. 

 Perhaps some of the microscopic and readily closed openings were exhalant. 

 On the other hand, it appears more likely that most of the sponge was in- 

 halant, and all the water from the canal system found its outlet at the 

 single exit. Another hole on the rhizome resembles an oscule, however. 



The ectosome is dense in structure with tangent spicules in abundance. 

 The endosome contains a reticulation of spicular tracts, 35 [x to 63 /x in di- 

 ameter, 20 to 50 spicules per cross-section. These outline meshes are often 

 about 300 n in diameter. Between and among the fibers, there is a vague 

 isodictyal reticulation of spicules, and there are spicules in confusion. 



The skeleton comprises two distinct categories of megasclere. There 

 are large oxeas, 11 /x by 290 \x, and strongyles, often somewhat curved, 6 n by 

 60 ll to 8 /x by 100 /a. The microscleres are palmate isochelas, 18 /x to 20 fx long. 



This species is set off by the generic characteristics, as already discussed. 



The species name is derived from the Greek for "chimney." 



FAMILY AGELASIDAE Verrill 



GENUS A'GELAS, Duchassaing & Michelotti 



Agelas mauritiana (Carter) de Laubenfels 



Text Figure No. 72 



This species is here represented by the following : 

 U.S.N.M. No. 22961, My No. M. 335, collected June 28, 1949, by diver at 



Majuro Atoll at the north side of the lagoon near Enemanok Islet. The 



depth was 2 meters and the substrate was dead coral. 

 U.S.N.M. No. 22959, My No. M. 333, collected at nearly the same time and 



locality as the preceding. 

 U.S.N.M. No. 22997, My No. M. 375, collected July 7, 1949, by diver from 



the open ocean just off Rube Point at Ebon Atoll. The depth was 3 



meters, and the substrate was dead coral. 

 U.S.N.M. No. 22802, My No. N. 007, collected April 25, 1946, by J. P. E. 



