ART. 12 HEXACTINELLID SPONGES — OKADA 113 



Specimen B is not so well preserved as specimen A ; several parts 

 of the entire stock are torn off. The hypodermal pentactins are 

 more numerously veiled on the surface of the sponge. In this speci- 

 men, the prostal marginalia are better developed and can be distinctly 

 observed. Along the oscular edge the diactinic prostal marginalia 

 project straight upward, the exposed portion attaining a length of 

 30 mm. This spicule is very long, and is inserted for half or more of 

 its entire length in the sponge body. They are smooth on the surface 

 except the proximal ends, which are minutely tuberculated and taper 

 gradually toward the tips. In the discoctasters, the humplike prom- 

 inences of the central node usually appear and are distinctly 

 recognizable. The terminals of the oxyhexasters are not so fragile 

 as those occurring in specimen A and are very nearly like those of 

 the type specimens. 



RHABDOCALYPTUS BIDENTATUS, new species 



Figure 16 C) 



This new species is based on a single holotype specimen (United 

 States National Museum No. 22053). It is a fairly large, solitary 

 individual, obtained at Station 5087 in Sagami Bay (614 fathoms). 

 The body is cuplike in shape, truncated at the upper end and gradu- 

 ally narrowed toward the base. The height is 195 mm. The body is 

 only slightly laterally compressed. At the superior region of the 

 body the breadth is 95 mm ; near the base it is 45 mm. The oscular 

 edae is not so thin as in some other members of the genus and mav 

 not be provided with distinct prostal marginalia. The base is solid, 

 as the gastral cavity does not extend to the attachment surface. The 

 thickness of wall at the middle of the body is 10 mm ; farther below 

 it measures up to 2 mm and near the oscular margin it measures 

 7 mm. The dermal surface may be fairly smooth, when in a good 

 state of preservation. On the whole, it forms a delicate lacework, 

 judged from the remains of the meshes of latticework seen under the 

 microscope. Pentactinic hypoclermalia are mostly preserved in in- 

 ferior parts of the stock. On the inner side of the wall, the endo- 

 some shows a continuous delicate gastral lacework, the quadrate 

 meshes of which are visible to the naked eye. 



The incurrent canalar apertures are of about the same size as the 

 excurrent on the external side but are somewhat more closely set 

 together. They usually show an oval, sometimes elliptical, shape 

 and measure 2 mm to 7 mm. 



Our species closely resembles R. tmguiculatus Ijima but differs 



from it chiefly in the dermal spiculation and in the character of the 



terminal disk of the discoctaster, which has two distinct sharply 



pointed claws on its edge. The species also agrees with R. mirahilis 



118040—32 8 



