98 



CAMBEIAN BRACHIOPODA. 



Y. 



Present reference. 



yorkensis [Acrothele], Walcott [1908d, pp. 88-89] Acrothele yorkensis. 



Yorkia Walcott [1897b, p. 714] Yorkia. 



Walcott [1908e, PI. XI, and pp. 142 and 146] Do. 



Yorkiamiqueli Walcott [new] Yorkia miqueli. 



Yorkia? orientalis Walcott [1906, pp. 569-570] Yorkia? orientalis. 



Yorkia wanneri Walcott [1897b, p. 715] Yorkia wanneri. 



Yorkia? washingtonensis Walcott [1897b, pp. 715-716] Yorkia? washingtonensis. 



Z. 



zeno [Eoorthis], Walcott [1908d, p. 106] Eoorttis zeno. 



zenobia [Micromitra], Walcott [new] Micromitra zenobia. 



zetus[Obolus (Lingulella)], Walcott [1898b, p. 419] Obolus zetus. 



zeus [Lingulella], Walcott [new] Lingulella zeus. 



zoppi [Obolus?], Walcott [1901, pp. 684-685] .Obolus? zoppi. 



GEOLOGIC DATA. 

 GENERAL GEOGRAPHIC AND STRATIGRAPHIC DISTRIBUTION. 



The distribution of the Bracliiopoda, both Cambrian and Ordovician, is set forth in the four 

 tables following. The first (pp. 98-109) gives the general geographic and stratigraphic distri- 

 bution of the various Cambrian and Ordovician species, arranged zoologically; the second 

 (pp. 110-112) gives a summary of the Cambrian Brachiopoda by genera and by families; the 

 tliird (p. 113)- a summary of the Ordovician Bracliiopoda by genera and by famiUes; and the . 

 fourth (p. 113) a general summary by families of all the Brachiopoda described in this paper, 

 whether Cambrian or Ordovician. 



The question of the systemic reference of some of the formations (e. g., whether the 

 Orthoceras limestone and the Ceratopyge hmestone should be placed in the Ordovician or the 

 passage beds between the Upper Cambrian and Ordovician, or whether the Ceratopijge slate, 

 the Bryograptus slate, and the Dictyograptus slate should be referred to the Upper Cambrian or 

 the Ordovician, etc.) does not appear to be a vital one in connection with this monograph. 

 Wlienever possible, however, the locaUties included in these pages contain the names of the 

 formations represented, and these should enable the student to refer the species to the desired 

 place in the geologic column. 



DISTRIBUTION BY SPECIES. 



The following table gives the general geograpliic and stratigraphic distribution of the 

 Cambrian and Ordovician Brachiopoda taken up in tliis monograph: 



General geographic and stratigraphic distribution of the Cambrian and Ordovician Brachiopoda. 



a Type locality in italic. 



6 The exact stratigraphic position of this species is not definitely known. 



