No. 560] CAMBRIAN HOLOTHURIANS 495 



the chief ciliated band. In Eldonia the mouth is the more 

 central, and there appears to be a possibility that the 

 anus is on the dorsal surface above the fringed border. 

 The ciliated bands of Trochosphcera have a very definite 

 connection with the mouth, a connection not evident be- 

 tween the fringed border of Eldonia and the mouth, the 

 relationships in the latter being almost exactly like the 

 relationships between the digestive tube and the ex- 

 panded brim in such holothurians as Euphronides tan- 

 ner i. Although the superficial resemblance between El- 

 donia and Trocliosphmra (including trochophore larvse) 

 is certainly striking, I can not see the slightest reason 

 for connecting the two ; the relation between them is pre- 

 cisely similar to that between certain of the pteropods 

 and the nautilus, which, on account of their remarkable 

 similarity, were for a long while placed in the same 

 genus. 



2. Certain ''worms" have a digestive system suggest- 

 ing that of Eldonia; but such worms are never provided 

 with oral tentacles, possessing instead a tough protrusible 

 proboscis; nor do they ever have the digestive tube dif- 

 ferentiated as in Eldonia; nor do they ever have the body 

 of a type which, on account of the structure of the body 

 wall and the general internal anatomy, particularly the 

 type of muscular investment, could by any stretch of the 

 imagination be supposed to assume a bell-like form. 



Certain heteroradiate echinoderms, as some holothu- 

 rians belonging to the family Elpidiidae, a few echinoids, 

 and the (recent) endoeyclic crinoids, have a digestive 

 tube resembling very closely that of Eldonia, and in the 

 holothurians there are always tentacles about its anterior 

 end. Moreover, in many of the Elpidiidae, as, for instance, 

 in Euphronides tanneri, the body is entirely surrounded 

 by a broad brim with marginal lappets, just as it is in 

 Eldonia. 



Judging from all the evidence which we have — and the 

 specimens of Eldonia are among the most wonderfully 

 preserved fossils which have ever come to light — Eldonia 



