42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



TEXT FIGURES 



PAGE 



Figure 2. Diagrammatic reconstruction of the imagined primitive Pel- 



matozoic ancestor 43 



3. Diagrammatic reconstruction of imagined Dipleurula ancestor 43 



4. Diagrammatic reconstruction of the imagined primitive Holo- 



thurian type 44 



5. Eldonia ludivigi, X i 47 



6. Synaptula hydriformis (Lesseur) 54 



INTRODUCTION 



The first paper on Middle Cambrian fossils from British Columbia 

 included the description and illustration of some new types of 

 Merostomes.^ This paper contains a preliminary notice of the dis- 

 covery of certain forms of Holothurians and one new Medusa. 



That the tests of Trilobites and Merostomes should be finely pre- 

 served in a fine-grained, silico-argillaceous rock is rather to be 

 expected, but with past experience in view I was not prepared to 

 find entire Holothurians. That they are present and show many 

 details of structure is most instructive and satisfactory, since their 

 occurrence records for the first time, with the exception of some 

 scattered calcareous spicules and plates, the presence of this class of 

 organisms in any geologic formation. Any calcareous matter that 

 may have been present in thein was probably removed by solution 

 while the animal was in the mud and before it became fossilized. 

 That carbonic acid gas was present in the mud and immediately 

 adjoining water is suggested by the very perfect state of preserva- 

 tion of the numerous and varied forms of life. These certainly 

 would have been destroyed by the worms and predatory crustaceans 

 that were associated with them, if the animals that dropped to the 

 bottom on the mud or that crawled or were drifted onto it were not 

 at once killed and preserved with little or no decomposition or 

 mechanical destruction. This conclusion applies to nearly all parts 

 of a limited deposit about six feet in thickness, and especially to the 

 lower two feet of it. 



The stratigraphic position of the shale carrying the fossils 

 described is given in a section of the Ogygopsis zone of the Stephen 

 formation published in 1908.^ 



^Smithsonian Misc. Coll., Vol. 57, No. 2, 1911, pp. 18-28, pis. 2-7. 

 "Walcott, 1908, Smithsonian Misc. Coll., Vol. 53, No. 5, pp. 210 and 211. 



