THE SPONGES OF THE WEST-CENTRAL PACIFIC 135 



grooves, about 2 or 3 pores per mm. Definite exhalant openings or oscules 

 could not be established. 



The ectosome is very sharply set off and easily detached. It is charac- 

 terized by color and is packed with detritus. The endosome contains foreign 

 material but not to so large an extent. The spicules in it are chiefly arranged 

 in confusion. 



The skeleton, other than the foreign material (especially sand) comprises 

 smooth oxeas, 2 //, by 130 fi, and small sigmas, 15 /x in chord length. 



This species was first described as Chondropsis ceratosus by Kirkpat- 

 rick, 1900, page 355, from the East Indian region. It was transferred to 

 Psammascus by de Laubenfels, 1936, page 99. It bears considerable re- 

 semblance to a sponge which was described as Phoriospongia canaliculata by 

 Lendenfeld, 1889, page 602, from the Australian region. The latter, how- 

 ever, is lobose to frondose, whereas ceratosus is incrusting. These Ponape 

 specimens obviously had every incentive to be ramose, yet the sponge showed 

 no tendency to grow in that direction but merely to spread indefinitely as a 

 thin crust. An interesting suggestion occurs ; namely, that Lendenfeld's 

 specimen might have been similarly incrusting over some substratum which 

 he did not notice. In this case, the later name ceratosus would have to fall 

 in synonymy to the earlier name canaliculata. This step is not taken at the 

 present time. 



FAMILY MICROCIONIDAE Hentschel 



GENUS THALYSIAS Duchassaing & Michelotti 



Thalysias cervicornis (Thiele) de Laubenfels 



Text Figure No. 86 



This species is here represented by the following : 

 U.S.N.M. No. 22892, My No. M. 192, collected August 3, 1949, by diver in 



western Ponape at Jokas near Tavak passage from a reef barely inside 



the lagoon. The depth was 8 meters, and the substrate was dead coral. 



This species was very abundant in this vicinity. 

 U.S.N.M. No. 22905, My No. M. 209, collected August 13, 1949, by diver 



in the west part of Truk lagoon, specifically at Lemotol Bay. The depth 



was 2 meters and more, and the substrate was dead coral. The species 



was very abundant in this vicinity. 



The shape is sprawling ramose. The diameter of the branches is 6 to 

 10 mm. The length is often 30 cm and in some cases as much as 70 cm. 

 The branching is very peculiar. Considerable areas have no branches, and 

 when they occur they may be at right angles. Numerous extremely short 

 branches, some of which are scarcely more than tall conules, are also found 

 in places. 



The ectosome and endosome color in life in the specimens in Ponape 



