40 C. D. Walcott — Position of the Olenellus Fauna. 



Middle Cambrian. As far as the specimens of O. Marcoui of 

 the Lower Cambrian will permit of comparison, it and O. 

 Ffevadensis of the Upper Cambrian are closely related. 



The two species of Zacanthoides, Z. Eatoni and Z. levis, are 

 representative species of the genus, and serve to unite the 

 fauna with that of the Middle Cambrian, as Z. tyjncalis and 

 several species occur in the Middle Cambrian of the interior of 

 the continent. The genera Bathynotus, Avalonia, Orycto- 

 cephalus and Protypus are peculiar to the fauna and do not 

 appear to be represented in the Middle or Upper Cambrian. 



Conocwyphe trilineata is one of the best marked forms in 

 the New York Lower Cambrian, and is closely related to C. 

 elegans and C. coronata, of the Paradoxides zone, in having 

 the same general form and in the absence of eyes. The genus 

 Ptychoparia is represented by nine species, all of which are 

 more or less closely related to forms in the Middle and Upper 

 Cambrian. 



Agraulos strenuus is represented in the Upper Cambrian by 

 A. socialis. Ellvpsocephalus WordensMoldi, of Sweden, is 

 represented by E. Hoffi of the Paradoxides zone of Bohemia. 

 Crejpicephalus Augusta and C. Liliana are types that are more 

 or less abundant in the Upper Cambrian fauna of the interior 

 of the continent. They are not represented, to my knowledge, 

 in the Middle Cambrian fauna. The small head that I have 

 referred to Anomocare parvum may be compared to A. sulca- 

 tum of the Paradoxides beds of Sweden. The genus Soleno- 

 pleura, with its five species, is also well developed in the Middle 

 Cambrian fauna. S. Howleyi, from the base of the Olenellus 

 zone of Newfoundland, is very closely related to the type of 

 the genus, S. holometojKt, of the Paradoxides zone of Sweden. 



Comparison of the Faunas as a whole. — The first thing 

 that strikes one in comparing the fauna of the Olenellus zone 

 with that of the Middle Cambrian is that the latter is not 

 wholly known, or in other words, there existed somewhere a 

 Middle Cambrian fauna which has not yet been found. "We 

 are now obtaining evidence of a considerable fauna that lived 

 during Middle Cambrian time, on the west or Pacific coast of 

 what then existed as the North American continent, and of 

 which there is scarcely any representation in the Middle Cam- 

 brian or Paradoxides fauna of the Atlantic Province. This 

 will add to the fauna, but there is still a notable absence of 

 certain forms in the Middle Cambrian fauna which are present 

 in the Lower Cambrian. The first noticeable exception is the 

 absence of representatives of the peculiar group of corals that 

 occur in the Olenellus zone. With a single possible exception 

 the Archseocyathinee are not represented in the Middle Cam- 

 brian. 



