90 PROCEEDINGS OF THE NATIONAL MUSEUM vol.81 



The distal ray is the smallest and shortest of all, measuring ISOfx to 

 220/x, in length and sharply pointed at the end, while the paratangen- 

 tials are usually somewhat longer and bigger than the distal ray, 

 200/x to 240/x long. 



The oxyhexaster consists of normal oxyhexaster and hemihexac- 

 tinic and hexactinic forms. The normal oxyhexaster is abundant, 

 measuring 125)li to IGO^ia in diameter. Two varieties of this spicule 

 can be distinguished from the characters of the ray; both seem to 

 occur together promiscuously. In the one the center is swollen to a 

 globular shape, and the very short principals are somewhat rounded 

 in a knoblike manner. Terminals are slender, mostly rough but 

 occasionally smooth, usually three or four arising from each princi- 

 pal. It seems that this is the more abundant of the two oxyhexaster 

 varieties. 



In the other form the terminals are usually two in number and 

 slightly stronger, while the principals are much less distinctly indi- 

 cated, being in fact quite abortive. Insignificant microtubercles are 

 sometimes seen on the surface of the terminals. They measure 

 usually 110/A to 115/^ in diameter. 



Hemihexactinic and hexactinic forms are also intermixed with the 

 normally developed oxyhexaster in the choanosome of the sponge 

 body. They measure 120/x to 160;a in diameter. The terminals, which 

 look moderately strong, are about 10/x thick at the base, and their 

 surface is obsoletely rough. The latter occurs usually much more 

 abundantly than the former. 



The macrodiscohexaster resembles that occurring in A. ijwiai 

 (Schulze). It is sunlike in appearance, measures nearly 200/* to 

 430/x at the axis of the rosette, and is present mostly in the choano- 

 some. 



From the end of the principals, which are separated by six hemi- 

 spherical bosses measuring 45/x to 55^ across, there arise numerous 

 very long and slender terminals, radiating uniformly outward. 

 Terminals are filamentlike, obscurely rough-surfaced, and furnished 

 with a disk at the end, which is somewhat conically convex on the 

 outer side. It measures about 12/i, in diameter. The margin shows 

 a row of numerous small teeth. 



Microcliscohexasters of spherical shape and 40ju, in diameter are 

 not uncommon in or near the endosomal layer. They were occa- 

 sionally observed in the ectosome also. From a nearly spherical node 

 arise comparatively thick principals, which in length are about one- 

 third the radius of the rosette, each of which carries at the outer end 

 a small disk, usually provided with a central tubercular prominence 

 on the external side. The terminals are very fine and difficult to 

 count, but there are probably not more than 10 to each principal. 



