LETTCOPSACID.E. ol 



not with any other family. The absence of distal ra3's to the 

 dermalia, it may be said on theoretical grounds, is simply due 

 to a secondary loss, which might be easily conceived if we 

 remember the great variability of the corresponding spicules 

 within the family Rossellidie. It may bo that the pentactinic 

 dermalia, as I'epresented in quite young Regadrella okiiw^ea/ni 

 (Lt., 'oi, p. 240) probably as the result of adaptation to certain 

 secondary circumstances and which in this Euplectellid are soon 

 overcrowded by later formed hexactinic forms, have in the present 

 cases become permanent under the continuance of the same 

 adaptive conditions. It is certainly not to l)e excluded that 

 hexactinic dermalia develope in certain limited parts of the body- 

 surface ; thus, in Placopegma solutum, according to F. E. Schulze 

 ('95» P- ^'-^)j the dermalia on the oscular margin are hexactins, 

 instead of pentactins as on the general surface. At all events it 

 appears justifiable to assume that the four genera under considera- 

 tion, whether separately or as a group, were derived either 

 secondarily from the Euplectellidiç or from an early prototype of 

 the same. With the progress of our knowledge in the future, it 

 may become necessary to incorporate them all or in part in the 

 family just referred to ; but meanwhile, I consider it expedient 

 to keep them separate in a distinct family, to be designated the 

 Leucopsacidie, even if only to avoid disturbing the integrity of 

 the Euplectellidœ as already defined. 



As regards the genera Leucopsacus and Cliaunoplectella, it 

 seems nothing stands in the way of regarding them as forming 

 a systematically coherent group which may have very early 

 diverged from the Euplectellid Corbitelline phylum. But now, 

 in associating with tliem the genera Caulocalyx and Placopegma 

 in one taxonomic group, I am not without misgivings as to whether 



