4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 70 



api)ear to be narrow elongate pieces and al)ont as many as there are 

 ambulacrals, with which they alternate. The mouth area is not 

 preserved. 



The interambulacral areas of the upper disc are composed of 

 slightly convex, usually six-sided plates, which are rather large in 

 comparison with the size of the animal. Of these there appear to be 

 between 120 and 130. From one to two, and at times three, diplo- 

 pores cross the sutures of each plate angulation, and these are far 

 more distinctly seen on the inside of the plates because of the pairs 

 of sharp but tiny spiracle elevations (text fig. i B, and pi. i, fig. 3). 

 The anal pyramid is unknown. 



The plates of the under side of the animal are also non-imbricating 

 and apparently in the main six-sided ; they appear to be somewhat 

 smaller than those of the upper side. Their number seems to be 

 between 140 and 160. In the center of the under surface there is 

 a comi)aratively large centrodorsal plate, about 2 mm. in diameter, 

 around which there is a ring of 10 elongated plates (pi. i, figs. 2 and 

 4, text fig. I A). All of the i)lates of the under surface are finely 

 ])itted, and these are arranged obscurely in lines across the sutures 

 of adjoining plates. They are too delicate to be remnants of vanish- 

 ing diplopores, and are probably nothing more than the similar 

 ])ittings seen in many cystids (pi. i, fig. 3). 



As the specimens come in two sizes and on difl"erent horizons of the 

 Lower Cambrian, the name Stroniatocystites walcutti is api)lied to 

 the larger form above described, of which 6 individuals are known. 

 The smaller ones are far more common, 25 being at hand, and they 

 vary in diameter from 9 to 15 mm. Because of their smaller size 

 they are here distinguished as variety minor. All that is i)reserved 

 of these smaller* specimens is the impressions of the marginal plates 



(pi. i.fig. 4)- 



Locality and Jwriaon. — In the Olenellus beds of the Lower Cam- 

 l)rian (Taconian) of East Arm of Bonne Bay, western Newfound- 

 land. The type material is in the collection of the U. S. National 

 Museum, catalogue numbers 66443, 66444. 



Remarks. — Bather states that Stroniatocystites " was probably 

 sessile on its under surface but perhaps not fixed permanently." The 

 word sessile may be interpreted as meaning sitting upon, or attached 

 to something, and it is in the former sense that we must here accept 

 the significance of sessility. In both the European and American 

 forms, the under thecal surfaces do not show the slightest scar or 

 modification such as would follow if the animals were firmly attached 



