94 I. IJIMA : HEXACTIXELLIDA. I. 



relation to the prevailing direction of the movement of the sur- 

 rounding medium. The lateral compression of the body, especially 

 at the base, in so many other Lyssacine Hexactiuellids may 

 possibly fall under the same category of phenomena. 



For the rest the basal tuft penetrates into the sea-bottom 

 and represents an irregular, elongate and often bulky mass, in- 

 closing a fair sample of the bottom (fragments of sponges, 

 Bryozoa, Mollusca, &c.; sand and pebbles). The lump is frequently 

 much longer than the sponge-body proper. I can not tell 

 whether or not, it is simply due to the loose character of the 

 substratum in tliis case, that such a large basal mass is taken 

 up with the sponge. 



The appearance of the wall on the gastral side (PI. IV, 

 iig. 4) is essentially the same as in other Euplectella. The 

 transverse ridges are on the whole well set apart from one another, 

 notwithstanding the frequent occurrence of anastomoses by means 

 of obliquely running ridges. The longitudinal ridges show less 

 regularity of arrangement in so far as they often run in pairs 

 unusuallv close together. Such double ridges occur without 

 definiteness as to their position. The two may remain nearly 

 unchanged in relative position throughout their entire length ; at 

 other times they may in their course either fuse into one or 

 diveroe into two indubitablv distinct rido-cs. 



O %j CD 



Close to their juncture with the sieve-plate, the transverse 

 ridges are usually scarcely recognizable as such. Wo. rather see 

 here only obliquelj^ and longitudinally running ridges or beams, 

 which above pass directly into the formation of sieve-plate beams 

 (upper j^art of iig. 4). 



The beams of the skeletal framework, Avhich form all the 



