452 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



5 mm., which extends to the lower end of the sponge. The cloaca 

 opens to the exterior not only at the terminal osculum, but by means 

 of lateral diverticula at three other oscula as well. Two of these 

 are near the upper end, one near the lower. All the oscula (pseud- 

 oscula, as they would more properly be called) are of about the 

 same size. Sponge stony ; pinkish-brown. 



Pores in the rounded meshes of a skeletal reticulum that is formed 

 by the overlapping clads of the ectosomal phyllotriaenes. Meshes 

 of the reticulum 150-200 pi in diameter; two or three pores, some- 

 times only one pore, in each mesh. 



The tetracrepid desma (pi. 49, figs. 11, 15) starts out as a triaene. 

 The four primary clads, which become more or less branched, make 

 bold curves, bounding different skeletal meshes. They become 

 tuberculate at the ends where they enter into zygosis. The primary 

 clads frequently but not always bifurcate, and the secondary branches 

 again may send out short branches; all branches tuberculate at the 

 ends, zygosis being terminal. Primary clads about 35 \k thick. 

 Length of undivided clad 100-175 [x. In a bifurcated clad, primary 

 branch 75-125 \l long, secondary branches 50-140 [x long. 



The dermal phyllotriaenes (pi. 49, fig. 12) form a single layer. 

 Rhabdome is about 150 by 20 [x, tapering to a point. Typically 

 there are three narrow primary clads which branch irregularly, the 

 spicules being, thus, not far removed from the dichotriaene type. 

 There is considerable variation, however, as regards details. One 

 of the primary clads may not branch, while the others do. Or a 

 primary clad may simply widen out into an irregular termination 

 instead of branching. The secondary clads often do not branch, or 

 some branch and others do not. Occasionally there may apear to 

 be four main clads, but this is probably due to bifurcation of one of 

 the three primary clads close to the center. Length of clads variable ; 

 primary clads commonly 100-200 [x long, 35 [x wide; secondary dads 

 commonly 75-150 [x long. 



The membrane lining the cloaca includes phyllotriaenes. which 

 may be designated gastral phyllotriaenes, arranged in a single layer 

 with rhadomes vertical to the surface. They (pi. 49, figs. 13, 14) 

 are of a different type from those of the dermal surface, varying 

 toward the discotriaene form. Rhabdome 60-90 by 12-14 [x. The 

 cladomes which overlap in an irregular way are greatly flattened and 

 very thin. They vary from that of an ordinary phyllotriaene with 

 dichotomous clads to an irregular platelike cladome in which clads 

 are not distinguishable. Often three primary clads are present in 

 the shape of stout wide lobes which expand terminally but are not 



