240 ANNALS NEW YORK ACADEMY OF SCIENCES 



The "Permo-Carboniferous" extends also to the northward, where it 

 outcrops extensively in southern Idaho and also in Wyoming. There is 

 every reason to believe that in this region also the three formations of 

 the "Permo-Carboniferous" occur, for there is a remarkable agreement 

 faunally, stratigraphically and lithologically between the beds in southern 

 Idaho and in the Park City district. Indeed, they have already been 

 mapped in Idaho by Veatch. Furthermore, the "Permo-Carboniferous" 

 of southern Idaho contains the strata furnishing the ammonite fauna 

 which Hyatt and Smith have assigned to the lower Trias. The ammonite 

 beds occur at the horizon of the Tha}Ties limestone, which is convention- 

 ally taken to begin with the lowest ammonite zone. In this region, the 

 lower red shale corresponding to the Woodside contains thin limestones 

 having a fauna which agrees closely with that of the Thaynes. ■ Thus 

 the three members of the "Permo-Carboniferous" are related faunally 

 and form a natural lithologic group also, with distinct boundaries above 

 and below, especially the latter. This instrinsic relationship of the rocks 

 found expression in their inclusion by the earlier geologists in a single 

 formation or series.- 



Although the evidence is not yet in shape for presentation in detail, 

 it seems all but certain that the "Permian" of the Grand Canyon area, 

 the "Permo-Carboniferous" of the Wasatch Mountains and the "Lower 

 Triassic" of southern Idaho are a single series of strata originally con- 

 tinuous from one region to the other and having essentially identical 

 faimas. The whole group, therefore, must be either Permian or Triassic. 

 It remains for a more careful and critical survey of the evidence to 

 determine which. 



Aviculipecten ? boutwelli sp. nov. 



Shell small, subovate, a little longer than wide. Hinge line more than one 

 lialf the greatest width, which is found about midway. From there the shell 

 contracts rather regularly in both directions. The ventral outline is narrower 

 than the cardinal and strongly rounded. The sides straighten somewhat 

 toward the hinge or even bend slightly outward but without producing any 

 distinct sinus. While fairly symmetrical, the greater development appears to 

 l)e on the anterior side of the shell. Convexity moderately strong, especially 

 about the umbo. Beak subcentral, small, incurved. Wings about equal, un- 



- The relationship of the beds in southern Idaho with the "Permo-Carboniferous" was 

 recognized in a general way by the earlier geologists. The relation was more satisfac- 

 torily demonstrated several years ago by collections of fossils made by F. B. Weeks and 

 reported on by me. It was not until the season of 1900 that evidence was obtained, by 

 a party In charge of II. S. Oale, with which I had the pleasure of being associated, 

 showing that the lower Triassic ammonite fauna occurs within the limits of this series. 

 After his work in southern Idaho. Mr. Oale visited the typical section of the Park City 

 district, verifying the close lithologic and sequential relationship which exists between 

 the beds in the two areas. 



