NO. 1 A LOWER CAMl'.KIAN EDKIOASTERin SCIIUCHERT 7 



il the Strniiiatocystifrs. The animals had to haltlc constantly ai^ainst 

 this (lani^cr, and throus^h the aid of their breathin_i;- podia probably 

 did dii^' themselves out when accidentally covered by the muds. Sucli 

 treatment often repeated, as it must have been, mi,i;ht well have been 

 the stimulus that brought about forms that learned how to creep 

 around on their nutrient ambulacra! surface through the aid of their 

 breathing" podia. In this way breathing" podia were changed into 

 locomotor podia like those of asterids. At the same time, the passive 

 funnel-like mouth of Stromatocystitcs evolved into the active preda- 

 tory organ of asterids. 



In the permanently overturned condition, with the mouth beneath 

 the disc, such as occurs in a form similar to Stroiiuifocystitcs, Bather 

 states that the hydropore and anus would have to migrate along" the 

 posterior interracHus toward the aboral pole, and in consequence the 

 stone-canal would become elongated. I'he ambulacra and the cover- 

 in,i^ plates became the ambulacra and adambulacra of asterids. On 

 the other hand, the side ])lates of edrioasterids appear to be new 

 structures not jiresent in dii)lopore-cystids, and they may well be the 

 equivalents of the inframarginalia of primitive Paleozoic asterids. 

 Ilie mouth frame in edrioasterids is composed of 15 plates (the 

 live interradials are here fused plates, so that originally there were 

 10 of them), while in starfishes the more primitive form of 20 pieces 

 is often retained. All were originally ambulacral and intcrambulacral 

 ( =adambulacral) structures. 



