92 THE SPONGES. 



the under surface, which appears smooth as compared with the upper, 

 are roots 1-2 mm. thick, and 6-10 mm. apart, which are broken off close 

 to the body. The color of the interior and surface is brown, except where 

 the whitish collenchyma shows, the upper surface appearing dark because 

 of the mud held by the surface covering of spicules. The horizontal 

 diameter of the specimens varies from 40 to 60 mm., the vertical diameter 

 including the projecting spicules from 20 to 25 mm. 



The pore areas vary in number from 4 to 7, are mostly elongated in 

 the horizontal plane of the sponge, but in some cases are nearly circular. 

 The height of the areas varies from 5 to 9 mm., the width from 5 to 

 25 mm. They are depressed, and show the usual tumid whitish border. 

 In some areas the upper margin is provided with a well-developed fringe 

 of spicules, projecting about 5 mm. In other areas the fringe is absent, 

 unless, indeed, it be thrown back and merged in the general spicular 

 covering of the upper surface. The under margin of the areas in general 

 lacks a special spicular fringe, but here and there such a structure reaches 



a feeble state of development. The pores, 85-340 /x in diameter, 



are mostly open, and the pore membrane appears as a coarse reticulum 

 (Fig. 9, Plate 12). But in some cases the pores are partially or com- 

 pletely closed, the membrane appearing nearly or quite imperforate. In 

 the latter condition it is white and opaque. The pore membrane closes 

 in a subdermal space, from which large canals pass into the interior. 



The ectosome is collenchymatous, and about 0.5 mm. thick. The body 

 in general is excavated by numerous canals of comparatively large size. 

 The collenchyma round the larger canals is scanty. The flagellated cham- 

 bers are eurypylous and large ; many spheroidal, and about 70 jx in diam- 

 eter ; others more or less compressed, often strongly so, and measuring 

 about 80 /u- X 40 /x (artefact?). In sections fine canals (Fig. 2, Plate 12) 

 may here and there be seen extending radially through the ectosome and 

 opening on the surface by single apertures. 



Me(/asckres. 



1. Dichotriaene, Figs. 2, 7, Plate 12. The rhabdome is 100 fx thick just 

 below the cladome, tapering evenly to the point, often somewhat curved, 

 and about 6 mm. long. The protocladus is straight, tapers centrifugally, ' 

 and measures about 140 /a x 85 /x. The deuterocladi are in general curved, 

 first out, then in, as in Fig. 7, Plate 12, taper evenly to the point, and 

 measure about 960 /x x 70 /a. 



I 



