NO. I A LOWER CAMBRIAN F.DRIOASTERTn SCTTUCTTERT 5 



or cemented to the ground. Of course they were not errant animals, 

 but were, rather, stationary in habit and loosely anchored to the 

 muddy and sandy sea bottom by the concave under side and the down- 

 ward projecting margin of the theca. This naturally was a rather 

 precarious footing in a shallow sea, and undoubtedly the storm waves 

 often pulled them away from their moorings. 



In regard to disposition among the Echinoderma, Stronmtocystitcs 

 is at first sight somewhat perplexing. On the one hand, it is clearly 

 related to the diplopore-cystids in its thecal structure, and the five 

 ambulacra appear to be nothing more than modified recumbent 

 brachioles attached to the thecal plates. Yet it is not one of these 

 cystids, because Stroniatocystitcs was a free animal devoid of a stalk, 

 though retaining at times centrodorsal plates. On the other hand, 

 the genus is clearly on the line of evolution to the sessile edrio- 

 asterids, but is an unattached although not an errant form. That 

 Stromatocystites is already plainly on the line toward the edrioas- 

 terids is indicated by the structure of the ambulacra. This is seen in 

 the modification from the diplopore-cystids, where the free brachioles 

 are composed of two columns of alternating thick ossicles having 

 their ambulacral furrows covered over by two rows of roofing plates. 

 These four columns of ossicles are, in the genus under consideration, 

 the equivalents of the roofing and flooring plates of the ambulacra, 

 but there are in addition, the two columns of side plates, a new- 

 development not present in the brachioles of diplopore-cystids. In 

 these features we therefore seem to see how a diplopore-cystid 

 changed into the loosely anchored Stromatocystites, at the same time 

 trending in development toward the true edrioasterids. 



In 1905, Jean Miquel described a new form as Stromatocystites 

 cannati,' from a single specimen. It comes from the Middle Cam- 

 brian of the Montague Noire of France, and is peculiar in having 

 a much modified lower rim. Miquel says that the margin has very 

 large rectangular plates, and that each of the sides of the pentagonal 

 disc has from 3 to 5 of them. As the specimen is somewhat 

 crushed, and as an uncrushed side of the pentagon has 5 large 

 marginal plates, this may be taken as the actual number, so that there 

 were about 25 much modified ossicles in the anchoring rim of the 

 lower side. The lower thecal side is not described and is probably 

 unknown. " The ambulacra," Miquel says, " attain the extremity 

 of the circumference, and accentuate the angles of the pentagon ; they 



^ Bull. Soc. geol. France, 4th ser., vol. 5, 1905, p. 482, pi. 15, fig. 5. 



