4.Ki,12 HEXACTINELLID SPONGES — OKADA 107 



the letters A, B, and C. Forms A and C are chiefly in the ectosome 

 or endosome, and form B is common everywhere, intermixed with 

 other forms, though less numerous in the endosome. 



The A oxyhexasters (fig. 14, ff) are distinguished by having very 

 slender, slightly wavy and slightly roughened terminals. Each very 

 short principal usually carries two slightly curved terminals. The 

 diameter of the oxyhexaster, llS/x, seems to be greater than in 

 form B. Form A is not so numerous as the remaining forms. 



Form B (fig. 14, /) is 88/x to IOO/a in diameter and occurs every- 

 where. It is by far the best represented of the three forms, occurring 

 in greatest abundance of all these spicules. It is distinguished by 

 having nearly straight and rough terminals, which seem not to be so 

 fragile as those in the form A. Each very short principal is provided 

 with two, occasionally three, straight, slightly rough terminals. This 

 roughness becomes more or less pronounced toward the base, but not 

 so prominent as to form microspines or barbs. The terminals meas- 

 ure 48/A to 52/x long. 



Form C (fig. 14, e) resembles form B in shape and size. It is dis- 

 tinguished from the other forms by having very broad, strong prin- 

 cipals, to each of which are attached widely diverged strong termi- 

 nals. These principals are of a perceptible length, 4;ii; and there 

 are usually two, sometimes three, terminals to a principal. They 

 usually measure 49/x to 52ix long and have a smooth surface. This 

 oxyhexaster is represented in nearly the same numbers as form B, 

 but is more abundant in the endosome of the sponge. Throughout 

 the parenchymalia are a few oxyhexacts (fig. 14, d), which are rough 

 on the surface. The proximal and distal rays are 48/x long and the 

 tangential rays iO[x. 



Discoctasters (fig. 14, i) commonly occur among the paren- 

 chj'malia and are occasionally found in the ectosome, as well as in 

 the endosome. The six prominent bosses present on the central 

 node frequently form a large tuberculated mass, measuring 12/a by 

 18/x across. The principals are slender, at most 4^ thick ; about one- 

 half or more the length of the entire ray, measuring 20ft to 32/i, long. 

 The fine terminals are four to six in number, in a gently expanding 

 tuft measuring 16/x to 30/a in length, and have very minute terminal 

 disks shaped like a pinhead. The diameter of the spicule is 80[i to 

 120/x. 



The microdiscohexaster (fig. 14, ^) is relatively small, measuring 

 25/i in diameter. I have found it sparsely distributed everywhere, 

 though it is most frequently in the dermal and gastral membranes. 

 The principals are slender and form a cross measuring about Sfx in 

 axial length. The number of terminals may reach 10 to 12, meas- 

 uring 5/t long. 



