6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. JO 



are formed of two ranges of plates, small, regularly arranged, with 

 a quite large size, which decreases from the month of the animal to 

 their extremity. The species has in general form much analogy with 

 S. pentangiilaris Pompeckj." It differs clearly from this form "by 

 the size of the ambulacra and by the arrangement of the thecal 

 margin." 



Even this meager description shows that it is not a Strotnato- 

 cystites, but that it is plainly an edrioasterid. The marginal plates 

 are already those of edrioasterids. 



Relation to aster ids. — The edrioasterids are particularly interest- 

 ing fossils because the oldest forms seem to indicate the stock out of 

 which they arose, and at the same time appear to be near the forms 

 that gave rise to the asterids. Bather was the first to point out this 

 phylogeny and he has written at length about it. We will therefore 

 follow his argument. 



The oldest known asterids are of Middle Ordovician time, but here 

 there are already large forms in considerable variety, and the 

 structural differentiation among them is great.^ This of course must 

 mean a much older origin for the asterids. On the other hand, 

 edrioasterids go back to the late Lower Cambrian, and if the asterids 

 arose in the edrioasterids, we nuist look for small, subpentagonal, 

 diplopore-cystid-like, ancestral asterids certainly as early as the 

 Middle Cambrian and i^robably as far back as the Lower Cambrian. 



The origin of the starfish line may have been brought about, 

 according to lUither,' as follows: " If we imagine an edrioasteroid 

 with loose attachment, liable to be overturned by currents .... then 

 all we have to suppose is that some of the overturned individuals were 

 able to survive the accident. This they would be able to do if they 

 had fairly well developed podia, such as are indicated by the ana- 

 tomical evidence Indeed, it is hard to see how locomotion 



could have been avoided." 



The home of Stromatocystitcs, in both Euro])e and America, was 

 a shallow sea near a shore, where there was rapid accumulation of 

 sand and mud. Many of the strata of the Lower Cambrian of New- 

 foundland are rippled, and the organic and facial evidence is of 

 shallow seas, certainly less than 200 feet in depth, with the probability 

 of even less than 100 feet. In such a sea, the greater storm waves 

 could easily pick up the bottom and roll it about, carrying along with 



* See Schuchert, Revision of Paleozoic Stelleroidea, Bull. 88, U. S. Nat. 

 Mus., 1915, pp. 27-31. 



* Bather, Geol. Mag., dec. 6, vol. 2, 1915, p. 403. 



