40 T. IJIMA : HEXACTINELLIDA. I. 



parietal oscula are quite numerous and are distributed over the 

 entire lateral wall with a certain regularity, which is conditioned 

 by the arrangement of the principal skeletal beams as well as by 

 the course and the degree of development of the external ledges 

 soon to be noticed. 



The inferior terminal area of the body-wall, circumscribed 

 by the points of emergence of the basal spicules, either dies off 

 at an early stage — thus widely opening the tubular body at this 

 end — or persists as a thin soft plate, perforated by round oscula 

 as in the case of the lateral wall (PI. IV, fig. ö). This plate has 

 been described by writers as the inferior sieve-plate ; however, 

 in view of its aj^pearance which is widely different from the sieve- 

 plate proper, and also for the sake of more convenient reference, 

 I propose to call it simply the hottom-plale. It was first noticed 

 by Marshall ('75) in some specimens of G. aspergillum and 

 later by O. Schmidt ('80) in E. jovis and by F. E. Schulze 

 ('95) in E. simplex. I have observed it in both E. oweni and 

 E. marshaUi. 



The external surface of the sponge may be tolerably even 

 the interspaces between the parietal oscula being only gently 

 convex. In many species, however, these rise up into more or 

 less pronounced ridges, the parietal ledges, which generally run, 

 several nearly parallel together, along with one or another 

 of the three (circular, longitudinal and oblique) systems of the 

 skeletal beams, but they are subject to many variations and inter- 

 ruptions in their course (Pis. I, III, cfec). 



At the upper end of the lateral wall and along the junction 

 of this with the sieve-plate, there usually exists a collar-like 

 ledge in a continuous ring. This is known as the cuff (PI. II, 

 fig. 8), a formation which essentially agrees in origin and strue- 



