E. OKINOSEANA. — YOUNG SPECIMENS. 245 



resembles that of tlie young E. marshalli shown in PL IV, fig. 9 ; 

 the ledges are indicated by low reticulate ridges with rounded 

 edges, each depressed mesh containing a parietal osculum, of 

 which there are many. At the upper end exists a transverse 

 opening about 3 mm. wide. This is evidently the original single 

 terminal osculum of the specimeu. Directly adjoining it on one 

 side, but not on the other, is a small ill-defined area in which 

 the thin sponge-wall is perforated by several, somewhat closely 

 situated, irregularly angular gaps of various sizes. I take this 

 area to be a beginning of the sieve-plate formation. However, 

 I entertain some doubt as to whether I have seen it in quite its 

 natural condition, since the tissues at the parts bore signs of 

 laceration to a certain degree. 



Be that as it may, to my mind the first formation of the 

 sieve-plate in Euplectellidœ probably takes place in the manner 

 indicated. Thus, to the original single osculum at the upper end 

 of the sponge, more oscula are afterwards gradually added in 

 close proximity to it and to one another, converting the inter- 

 vening part of the body-wall into the sieve-plate beams. The 

 beams and nodes, after their establishment, may themselves also 

 become perforated and thus may contribute to the multiplication 

 of the sieve-plate meshes. 



6. Finally I will mention a specimen 70 mm. liigli and 20 

 mm. broad at the widest part. It is attached to the basal ex- 

 pansion of the same dead skeleton ou which the two young 

 specimens mentioned under (2.) and (3.) were found. The body- 

 form is peculiarly irregular, but this is undoubtedly due to 

 accidental causes. The ledges are tolerably well developed. 

 The upper end bears a definitely formed, but only slightly arched 



