S)jiiopsi's of the Aadrailau Oalotrea Heterucwla. 93 



a very inconspicuous fringe ; they attain a height of about 

 15 mm. and a maximum diameter of about 5 mm. The 

 texture is dense and firm, and the sui-face is roughened 

 by the projecting ends of some of the large oxea. 



The gastral cavity is narrow and cylindrica], occupying 

 only about one-third of the total diameter of the sjionge. 

 The flagelUited chambers are long and naiTow and more or 

 less radially arranged with regard to the central gastral 

 cavity ; they do not extend nearly through the entire thick- 

 ness of the sponge wall, and they communicate with tlie 

 gastral cavity through long, sometimes branched exhalant 

 canals. The inhalant canal system consists of scattered 

 pores on the dermal surface leading into elongated canals 

 which lead down between the chambers, but the typical 

 syconoid arrangement of the canal system is greatly 

 obscured by the strong development of the mesoderm 

 and the dense, irregular skeleton. There is a ver}- thick, 

 dense cortex on both dermal and gastral surfaces. 



The skeleton of the gastral cortex consists of a densely 

 felted mass of irregularly arranged triradiates, mostly lying- 

 parallel to the gastral surface. These spicules are sagittal, 

 with fairly stout, sti-aight, conical and graduall}' shar})- 

 pointed rays ; the oral rays are longer than the basal and 

 the oral angle wider than the other two ; oral ra3'S about 

 ()-lS mm. by 002 mm., basal about 012 mm. by 0010 mm. 

 The skeleton of the chamber layer is dense and irregular, 

 but shows traces of the articulate tubar arrangement in the 

 usually centrifugal direction of the basal rays of the tri- 

 radiates. These spicules are smaller than those of the 

 gastral cortex, and of different shape ; there is not much 

 difference in the length of the rays, though the basal may 

 be slightly longer or shorter than the others ; all the rays 

 are fairly stout, conical and gradually sharp-pointed ; the 

 basal is straight but the orals are more or less curved 

 towards one another; dimensions of rays about 012 by 

 0-OlGmm. 



The skeleton of the dei-mal cortex consists of a dense,, 

 confused mass of triradiates, resembling those of the 

 chamber layer but becoming markedly smaller towards 

 the outside, where they lie parallel to the surface ; amongst 

 which are found oxea of two kinds : — (1) Very large, stout, 

 fusiform, slightly curved and sharply pointed at each end ; 

 measuring about 18 mm. by O'l mm., and arranged parallel 

 to the long axis of the sponge, with the upper end often 



