MESOZOIC FOSSILS. 603 



Besides the species named, there are fragments of two species of 

 ammonites, and several other forms are represented by casts or other imper- 

 fect material. All of the species named in this list, excepting Goniomya 

 montanaensis, occur at various localities in the Park, as shown in the 

 annotated list of species (pp. 608-631). 



Comparatively few Jurassic fossils are known from Utah, and they are 

 probably all from one horizon. According to the various reports published, 

 as well as personal observation in both the northern and southern parts of 

 the Territory, the fossiliferous zone is a calcareous bed near the base of the 

 local Jurassic sections. In Weber Canyon it has yielded Gucullcea haguei, 

 Pleuromya subcompressa, Pentacrinus asteriscus, and a few other forms; in 

 Thistle Canyon the peculiar Lyosoma poivelli was obtained, and in a collec- 

 tion made by Mr. Robert Forrester on San Rafael River I have recognized 

 Trigonia americana and Pholadomya kingi, all of which occur in the Park. 

 For these reasons I regard all of the fossiliferous Jurassic beds now known 

 in Utah as belonging to the same horizon that is so well represented in the 

 Yellowstone National Park. 



The question still remains whether the Jurassic of the Black Hills 

 belongs to a higher horizon. There are some facts in favor of the opinion 

 that the Jurassic fossils of the two regions may not be contemporaneous. 

 For example, a number of the most abundant species in the Yellowstone 

 National Park region, such as Pleuromya subcompressa, Pholadomya kingi, and 

 Cypricardia haguei, have not been reported from the Black Hills. The 

 Yellowstone species of Trigonia, Modiola, and G-ervillia are also distinct. 

 Pseudomonotis (JEumicrotis) curia, which is one of the most abundant species 

 in the Black Hills, is represented in the Park collection by a single doubtful 

 specimen. No example of Cardioceras cordiforme has been found in the 

 Yellowstone National Park, and several other common Black Hills forms 

 are either absent or rare there. 



On the other hand, there is a considerable list of species common to the 

 two regions, among which may be mentioned: 



Pentacrinus asteriscus. Camptonectes belli striatus. 



Rhyncbouella myrina. Camptonectes platessiforniis. 



Ehyncbonella gnatbophora. Avicula wyomingensis. 



Ostrea strigilecula. Belemnites densus. 

 Grypbrea calceola var. nebrascensis. 1 



1 The Black Hills specimens of this species are all small. 



