80 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 81 



rangement as in A. fssuratus. In general they occur singly and 

 not in groups, the manner of arrangement being typically as de- 

 scribed below. The starlike texture of the sponge surface is mainly 

 formed by this pentactin, situated centrally with the diactins run- 

 ning along its paratangentials and entering with them into the sup- 

 port of the dermal layer. The pentactins are comparatively large, 

 with rather strong rays. They are infrequently supplied with a boss- 

 like rudiment of the distal ray, the end of which is strongly beset 

 with sharply pointed microspines. The paratangentials may be ISOfi 

 to 1,045|U, long and the unpaired proximal ra}^ 500|Li to l,TOO;ti long. 

 The rays at the base may attain a thickness of 45;a. The conically 

 pointed ends usually show a tuberculated surface. The diactins are 

 generally 20/i, to 30^i in breadth at the center and less than 3% mm in 

 length. They quite agree in appearance with the similarly sized 

 hypogastralia, except for the fact that the spicular center is often, 

 but not always, externally marked by an inconspicuous annular 

 swelling. 



The parenchymalia are all slenderer and longer diactins than those 

 of the hypodermal and hypogastral layers. They are usually 

 grouped together into curled, ill-defined bundles. The principalia 

 may attain a length of 8 mm or more and a breadth of SOft at the 

 middle ; they are of nearly the same breadth throughout and smooth 

 on the surface except for the conical, tuberculated ends. 



The dermalia are nearly the same as those of A. flssuratus. They 

 are predominantly pentactins and occasionally stauractins. The 

 rays of the pentactins (fig. 9, c), as measured from the spicular 

 center, are 110^ to 165/a long and 8/i. to 12/^ broad at the base. Their 

 surface is completely rough, the roughness being inost pronounced 

 near the conically pointed end. They are also commonly furnished 

 with a bosslike rudiment of the distal ray. Stauractins (fig. 9, d) 

 are only slightly rough all over. Their axial length is from 280/^ 

 to 450/4. The rays taper perceptibly toward the rounded or coni- 

 cally pointed tip and are almost uniformly thick ; at the middle they 

 are 8/* to 12/a thick. The meshes of the dermal latticework, which 

 may be composed of pentactins and stauractins, are fairly regularly 

 quadrate, averaging 143/^ in length of sides. Seen under the micro- 

 scope the dermal latticework is not regularly meshed throughout, es- 

 pecially on the dermal membrane of the oscular margin. 



The gastralia are predominantly rough hexactins (fig. 9, e, f). 

 The paratangentials usually measure 155jn to 190/i, in length and 

 15)u, to 18/x, in thickness at the base. The distal ray is nearly as long 

 as, or somewhat shorter than, the paratangential in the same spicule, 

 while the proximal ray is generally much longer; it may be 330/x 

 in length. Sometimes in the same spicule these rays are subequal, 

 but often there is a high degree of variation in the length of the 



