CAMBEIAN AND LOWER ORDOVICIAN. 101 



Although this fauna, according to our present knowledge, is the oldest known Cambrian 

 fauna, it includes representatives of the several classes of invertebrates which I will enumerate. 



Actinozoa. — The corals are represented by a very primitive form of Protopharetra, a small 

 form of cup-shaped Archseocyathus, and a small Ethmophyllum closely aUied if not identical 

 with EthmopJiyUum whitneyi (Meek), which occurs higher in the section. The latter is not a 

 notably simple or primitive form of the Archseocyathinse; on the contrary, it is nearly as far 

 advanced as any species known in the Cambrian. 



Vermes. — The annelid borings and trails that occur in and on the sandstones and shales 

 are much like those of the Middle and Upper Cambrian. 



MoUuscoidea. — ^The two species of brachiopods represent widely separated genera. Mick- 

 witzia occidens Walcott is one of the primitive forms of the Paterinidse, while Trematoiolus 

 excelsis Walcott is a typical form of the Siphonotretidae. The interval represented by the 

 relative development of Mickwitzia and Trematobolus is sufficient to convince us that we must 

 look far back in Cambrian or it may be pre-Cambrian time for the progenitors of the inarticulate 

 brachiopods. 



Pteropoda. — The forms representing Orthotheca are abundant, large, strong, and evidently 

 as well developed as those of the Middle Cambrian. 



Crustaceans. — The trUobites thus far found at this horizon are confined to two species of 

 the genus Holmia. One of them, Holmia weeksi n. sp., has many segments and is more primitive 

 than such forms as Olenellus tJiompsoni Hall and Holmia iroggeri (Walcott), of the upper portions 

 of the Lower Cambrian section. The other species, Holmia rowei n. sp., is of the same general 

 type as Holmia iroggeri. The absence of all other trilobite genera is the most marked feature 

 of this early Cambrian fauna. 



In the section 100 miles to the south, at Resting Springs, Inyo County, Cal., a brachiopod 

 closely related to Billingsella JiigTilandensis Walcott occurs 2,800 feet below the upper limestone 

 in association with the trilobite Hdlmia rowei. 



Comparing the species in the early Lower Cambrian fauna with the OleneUus fauna, in 

 strata 5,000 feet higher in the section, we find a marked advance in the variety of the later 

 fauna, but we do not know how much of this may be due to the absence, from our collections, 

 of genera and species that may have existed during the deposition of the earlier sediments. 

 In the earlier fauna of the Waucoba section the class characters of the Arthropoda, MoUusca, 

 MoUuscoidea, Vermes, and Coelenterata were developed, and while the study of the genera and 

 species adds a little more to our knowledge of the rate of convergence backward in geologic 

 time of the lines representing the evolution of animal life, it, at the same time, proves that a 

 very long time interval elapsed between the beginnings of life and the epoch represented by the 

 OleneUus fauna. 



This fauna is described by Walcott/^" in the Smithsonian Miscellaneous Col- 

 lections. In his latest contribution Walcott *^^ says: 



The evidence afforded by the few -traces of pre-Cambrian fossils is inconclusive as far as 

 deternaining whether their habitat was in marine, brackish, or fresh water. 



The fossUs from the Chuar group of Arizona are not sufficiently characterized to prove 

 their origin or habitat. The protozoan Cryptozoonf occidentale Dawson is very abundant in 

 Arizona, also in the Belt series of Montana, Alberta, and British Columbia. It occurs in lime- 

 stones similar to those deposited in the fresh-water lagoons of Florida, and similar to the lime- 

 stones of the lake deposits of the Tertiary formations of the Great Plains region of North America. 

 The fossils of the Beltina zone of Montana and Alberta could as readUy have been developed 

 in fresh or brackish waters. There is nothing about the crustacean remains incompatible 

 with their living in fresh water, in fact, the fragments indicate a form more nearly related to 

 the fresh-water Brachiopoda with very thin test, rather than the strong Merostome (Euryp- 

 terus, etc.). 



