LEUCOPSACUS' ORTHODOCÜS. 37 



nearly its entire length, side by side with or in more or less 

 close apposition to, a ray of adjacent hexactins (PL III, fig. 26). 

 The result is a parenchymal framework which, whether seen in 

 a transverse or a longitudinal section, presents approximately 

 rectangular or quadrate meshes bounded by straight beams ; hence 

 the name 1 have given to the species. The beams consist usually 

 of two, but sometimes of three, spicular rays running alongside 

 but not always placed compactly together. It is however by no 

 means infrequent to find some hexactins, situated in an indefinite 

 relation to their neighbors, thus disturbing the regularity of the 

 framework. This is no doubt due in a measure to the free state 

 of each separate spicule. 



The comparatively few diactins that occur as parenchymalia 

 are small forms, probably never more than 1.5 mm. in length 

 and 8 /'• in breadth near the center, wliich is always marked 

 externally by an annular swelling. The surface is smooth, but 

 towards the gradually attenuated ends, is roughened by micro- 

 tubercles sparsely present. More especially are the oxydiactins 

 to be found in the deeper parts of the wall, running either 

 isolatedly or comljined in weak bundles. 



In the basal disc and directly against the foreign surface to 

 which the sponge is attached, the parenchymal hexactins form a 

 thin, irregularly meshed, basicUdyonal plate. This is of essentially 

 the same structure and appearance as that I have described from 

 Eegadrella okinoseana and homeyainai (Contrib. I., pp. 231-232, 

 2(34). The medium-sized, rough hexactins, which go to compose 

 it bv being soldered together either directlv rav to ray or 

 by means of irregular synapticuUe, may have rays as thick 

 as 16//. 



