NO. I A LOWER CAMBRIAN EDRIOASTRRTD — SCITUCTTERT 3 



of alternating' covering plates highly arched over the ambulacrnm. 

 about as wide as long, and from ii to 13 in number. Pompeckj sees 

 podial perforations, but in the writer's specimens none such appear 

 to be present. Mouth on upper side, covered by a number of im- 

 perforate plates, of which 4 are large and peripheral, with several 

 smaller ones between them. In addition, there are others of the 

 ambulacra. Anus in the bivium of the upper side, and covered by a 

 pyramid of about 9 small ossicles. 



Genotype. — .S. pentangnlaris Pompeckj, Middle Cambrian of 

 Bohemia. 



STROMATOCYSTITES WALCOTTI, new species 

 Plate I, figs. 1-4; text fig. i A-D 



This new diplopore-like edrioasterid is the oldest one known, being 

 from the upper portion of the Lower Cambrian, When alive, these 

 animals sat somewhat anchored upon the sandy mud, but they were 

 in no way cemented to sea bottom nor to foreign objects. The loose 

 anchoring was by means of the sharply bent and closely folded, pro- 

 jecting marginal rim, which was pressed down into the mud, assisted 

 by the concavity of the under side of the theca (see fig. i D). 

 Impressions of this rim are of common occurrence on the weathered 

 rock surfaces, though the calcareous plates are usually dissolved awa}' 

 by the percolating waters (pi. i, figs. 2 and 4). The plates of the 

 rim were somewhat thicker and far more irregular in shape and size 

 than those of either the lower or upper discs. In fact, there is a 

 tendency to form a ring of large plates, with many smaller irregular 

 ones about them. None of the plates are imbricating. The under 

 side of the animal is slightly concave, while the upper one is de- 

 pressed convex. The body cavity is very shallow, probably less than 

 3 mm. in depth. 



Stromatocystites walcotti is subpentagonal in outline, with the 

 greater diameters varying between 18 and 22 mm. The ambulacra 

 are restricted to the upper surface, are comparatively narrow, but 

 with distinct and sharply elevated, nearly parallel sides which are 

 deep and straight and terminate in the angles of the i)entagon. The 

 ambulacra are roofed over by small covering plates whose detail is 

 not preserved. The ambulacral grooves are distinctly floored by two 

 columns of elongate alternating plates, numbering between 11 and 14 

 in each row. None of these plates is perforated (see pi. i, figs. 1-3 

 and text fig. i C). The side plates are not well preserved, but they 



