ACANTHASCÜS CACTUS. 147 



same specimen {cfr. PI. XI., figs. 16 and 17), as is tlie rule with 

 all Hexactinellids of similar shape and structure. All the ex- 

 current canalar apertures, in fact the entire gastral surface, is 

 covered over by a well diiferentiated endosome (PI. XI., fig. ig; 

 PI. XII., fig. 35). In this the gastralia are however never so 

 abundantly present as to form a continuous layer of latticework 

 by themselves ; so that, the endosomal meshes, which present 

 themselves as such to the naked eye, may be said to be freely 

 open, except for some fine and insignificant trabeculic of the 

 gastral membrane that may occasionally extend across them. The 

 said meshes are of about the same size and shape as those of the 

 hypodermal framework ; only they are generally more rounded at 

 the corners, while the beams inclosing them are perceptibly 

 thicker. These beams, so far as the skeletal parts are concerned, 

 consist in the main of the strands of hypogastralia, along which 

 there occur the gastralia proper in scattered distribution together 

 with numerous hexasters. Certain hypogastral strands are some- 

 what conspicuously thicker than the rest and can be traced 

 continuously for a considerable distance, pursuing an irregular 

 course and frequently intersecting others of similar strength. 



The sponge in the living state is colorless or whitish. The 

 texture mav be said to be rather firm. 



Spiculation. 



As to the spiculation I have l)ut little of importance to add 

 to what is alreadv known throii2;h the investis^ations of F. E. 

 Schulze. To that gentleman I am indebted for the gift of a 

 slide-preparation made from the type-specimen described in the 



