NO. 2 MIDDLE CAMBRIAN IIOLOTIIURIANS AND MEDUSA 47 



9). There were probably radial muscles and muscles of the enteric 

 canal and tentacles, but these have not been observed. 



Radial canals. — The system of radial canals is very striking, and 

 medusa-like. They radiate from a central ring- canal (cr) out to the 

 margin of the umbrella. The tube-like character is probably best 



Fig. 5. — Eldonia hidtvigi, X 2. A specimen flattened in the shale and pre- 

 serving the alimentary canal, oral aperture and tentacles, water vascular 

 system and traces of the umbrella. U. S. National Museum, Catalogue No. 

 57537- 



ul =: umbrella lobes crushed and macerated ; cr and re = central ring and 

 radial canals of vascular system; o := oral aperture; tt = pehatodigitate ten- 

 tacles ; oc ^ oral chamber ; oe = oesophagus ; s ^ stomach ; I = intestine ; x =1 

 approximate point of union of stomach and intestine. The latter is better 

 shown by hg. 2, pi. 10; and figs, i and 2, pi. 12. 



shown by fig. 3 of pi. 11. They are usually crushed down with the 

 alimentary canal and all traces there lost, but in several examples 

 some of the canals may be traced across the broad canal and out on 

 the disk beyond. On a few specimens (pi. 8, fig. 3) some of the radi- 

 ating canals merge into rings that line the inner side of the margin 

 of the alimentary canal. On the outside of the alimentary canal in 

 this specimen the flattened radial canals appear like narrow ribbons 

 or bands united by fine fibers that may be traces of concentric mus- 

 cles. Where the outer margins of the umbrella have been macerated 



