l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



pieces is tabulated the distinctions are found to have a tendency to 

 disappear. 



Most of the species now recognized from locality 54s are trilobites, 

 and they are represented by hundreds of specimens. Besides abun- 

 dance of individuals we also find that many genera are characterized 

 by prolific species. 



The brachiopods are represented by 9 species, falling within the 

 common Middle Cambrian genera, Micromitra, Paterina, Iphidella, 

 Lingulella, Acrothele, Acrotreta, and Wimanella. Acrothyra minor 

 is the only uncommon form. Gastropods are represented by Hclc'wncUa 

 and Hyolithes. 



The agnostids are represented by one species, which is closely 

 allied to other Cordilleran species common in the Middle Cambrian. 



The smaller trilobites are represented by two species of Pagetia and 

 a pygidium referred to Tonkinella. Oryctocephalus is sparingly rep- 

 resented, but the new related genus Oryctocephalites is more abundant. 

 On the whole the small forms constitute a minor element of the fauna, 

 however abundant the individuals may be. Next in size are the species 

 of ProcacantJioides, which genus underwent a great expansion. The 

 form that first attracts attention is the large new trilobite Taxioura, 

 which is represented by two species. 



The most characteristic forms are the 9 species of Ptarmigania 

 and the n species of the closely related Dolichometopsis. There is 

 only one pygidium of Bathyuriscus. The wide-brimmed forms, Alo- 

 kistocarella, Kochaspis, and Kochina, are well represented. Kootenia 

 is represented by 6 species. Specimens are numerous, particularly of 

 A", convoluta, ■ which occurs enrolled in several instances. Only two 

 pygidia of Olenoides were found. Poidsenia also is well represented 

 by excellent material including an entire individual. Finally the median 

 trilobite form is represented by Pachyaspis and Ehmaniella. Although 

 individuals are fairly abundant, the trilobites of this sort constitute a 

 less conspicuous element of the fauna than usual for Middle Cam- 

 brian beds. 



A clearer idea of the composition of the Ptarmigania fauna will 

 result from a survey of the accompanying plates than from a lengthy 

 discussion. When this is done, however, care must be exercised to 

 view only the species that are positively assigned to the Ptarmigania 

 fauna. 



An interesting characteristic of the Ptarmigania fauna in the 

 northern Wasatch region is the great development of granulosity. 

 Nearly all species are granulose, and all have stronger ornamentation 



