APPENDIX 315 



E. Receptaculites and Arch^ocyathus. 



In "The Dawn of Life" (1875), reference was 

 made to the singular and complicated organisms of 

 the Upper Cambrian and Ordovician systems known 

 as Receptaculites, which at that time was generally 

 regarded as foraminiferal, and is still placed by 

 Zittel, in his great work on Palaeontology, among 

 forms doubtfully referable to that group. It has 

 also been referred to Sponges, though on very 

 uncertain grounds. It has not, however, so far as I 

 am informed, been traced any farther back than the 

 Upper Cambrian (Calciferous), and no structural 

 links are known to connect it with either Eozoon or 

 Archaeozoon. For this reason it was omitted in the 

 text ; but I think it well to mention it here, and 

 to direct attention to it as possibly one of the 

 complex Protozoa which may be traced far back 

 toward the beginnings of life.^ 



Another primitive and generalized genus men- 

 tioned in the text is ArcJiceocyatJius of Billings, 

 whose headquarters seem to be in the Lower Cam- 

 brian, and which may probably be traced farther 

 back. 



^ Billings, " Palaeozoic Times.'' 



