482 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The spicules and sand grains at outer and inner surface constitute 

 a "sand cortex" about 700 ft thick (pi. 51, fig. 10, 8. <:). Fibrous 

 skeleton includes a reticulum in the middle layer of the sponge wall, 

 slender radial fibers (f. /.) diverging from this on both sides, and 

 very peculiar connectives. 



Skeletal reticulum in the middle layer of the wall is scanty, its 

 fibers charged with sand grains and spicules, and not much, if any. 

 thicker than the radial fibers. The radial fibers are slender, 85 [/. 

 and less in thickness, laden with sand grains and sponge spicules; 

 regularly arranged, projecting outward and upward, and about 400 \l 

 apart; frequently uniting in pairs to form a fiber of the mesial 

 reticulum. 



The connectives are long, slender, smooth, cylindrical fibers, of 

 very uniform thickness, 24 to 28 \i thick; without inclusions. They 

 are very abundant in all parts of the sponge, intertwining and cross- 

 ing one another and the main skeletal fibers (pi. 51, fig. 10: pi. 52. 

 fig. 1). They run in all directions, but very many extend parallel to 

 the surfaces of the sponge and thus cross the radial fibers; of these 

 again, very many extend lengthwise (vertically in the upright 

 sponge). The fibers branch dichotomously now and then, but only 

 very rarely. They are united with one another not by the anastomosis 

 of branches, but chiefly by short transverse bars of spongin (pi. 52, 

 fig. 1, .§//), to which the term synapticula (borrowed from the 

 Hexactinellida) may be applied. The synapticula, which only very 

 rarely contain inclusions (spicules), are abundant, and thus the fibers 

 are combined together in reticular fashion. 



These fibers are very long, but how long I do not know. Perhaps 

 they connect, as branches, lower down in the sponge with the system 

 of main fibers. Where they cross one another or cross the main 

 (including radial) fibers, the crossing fibers are commonly cemented 

 together by little masses of spongin (pi. 52, fig. 3, sp.). Here and 

 there, but only rarely, a connective is united to a radial fiber in the 

 way that is usual in horny sponges. This is true of fiber a (pi. 52, 

 fig. 1), the connective appearing to arise as a lateral branch from 

 the radial fiber. Occasionally the end of a connective is found con- 

 stituting a spongin expansion on the side of another, as in the case 

 of fiber a (pi. 52, fig. 5). Summarizing, it may be said that in this 

 species the connectives are represented by long, independent fibers. 

 which are united with the main fibers and with one another almost 

 exclusively by short bars of spongin (synapticula) or by little 

 masses of spongin. 



The connectives show a very narrow medullary streak; this is 

 more conspicuous near the end of the fiber than elsewhere (pi. 52, 

 fig. 5). The substance is stratified, as may be seen in side view of 



