46 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



The alimentary canal is large, coiled in a loose, flat spiral and 

 divided into an oral chamber, oesophag-us, stomach, and intestine, the 

 end of the intestine opening on the ventral surface. 



Specimens of the type species grew to a large size, 12 cm. in 

 diameter. This form was gregarious and lived in large numbers 

 in quiet waters in association with a large, free swimming crustacean 

 fauna. 



Genotype. — Eldonia ludwigi, new species. 



Stratigraphic range. — Limited to a stratum of dark siliceous shale 

 a few inches in thickness in the lower portion of the Ogygopsis zone 

 ( = Burgess shale), of the Stephen formation as described in 1908. 

 (See footnote on page 51 of this paper.) 



Geographic distribution. — On the slope of the ridge between Wapta 

 Peak and Mount Field, north of Burgess Pass, and about 3800 feet 

 above Field on the line of the Canadian Pacific Railway, British 

 Columbia, Canada. 



ELDONIA LUDWIGI, new species 



Text fig. 5; pi. 8, fig. 3; pi. 9, figs. 1-5; pi. 10, figs. 1-3; pi. II, figs. 1-3; pi. 12, 



figs. 1-3. 



Body disk-formed or depressed umbrella-shaped. Exumbrella with 

 about thirty clearly defined lobes that radiate from the center to the 

 edge of the disk. Each lobe has a slight depression or line down the 

 center that extends in from the outer margin from one-half to two- 

 thirds the distance to the center (pi. 12, fig. 3), This secondary 

 lobation gives about sixty slightly projecting, rounded lappets about 

 the margin of the disk. In small specimens flattened sideways in the 

 shale (pi. II, figs, i and 2), the secondary lobation is emphasized so 

 that the narrow lobes (of the 60 series) extend inward toward the 

 center. The lobation of the exumbrella is shown by fig. 5, pi. 9; 

 figs. I and 2, pi. II ; and fig. 3, pi. 1,2. 



The surface of the subumbrella has a broad band of concentric 

 muscle fibers that extends about half way to the center of the disk 

 (pi. 9, fig. 5). The fibers are very fine and do not appear to be 

 interrupted by any radiating divisions of the subumbrella surface. 



From the subumbrella surface the mouth, with two short ten- 

 tacles when expanded, extended downward. (See description of 

 oral chamber and tentacles, following.) 



Muscles.- — Of the muscular system only the concentric muscles 

 of the subumbrella surface have been seen, as mentioned (fig. 5, pi. 



