162 PROCEEDINGS OP THE PALEONTOLOGICAL SOCIETY 



of ground-sloth remains in the Rattlesnake Lower Pliocene of eastern Oregon 

 and in Lower Pliocene beds exposed along San Pablo Bay, California. 



RELATIONSHIPS OF RECENT AND FOSSIL INVERTEBRATE FAUNAS ON THE 

 WEST SIDE OF THE ISTHMUS OF PANAMA TO THOSE ON THE EAST SIDE 



BY IDA S. OLDROYD 



(Ahstract) 



The range of various invertebrate species of the marine provinces to the 

 west and east of the Isthmus of Panama is discussed, and attention directed 

 to forms common to both sides of the isthmus. The report includes a state- 

 ment concerning origin of certain of these species from a common stock, as 

 well as observations on former trans-Panamic marine connections. 



TROPITIDJE OF THE UPPER TRIASSIG OF CALIFORNIA 

 BY J. P. SMITH 



(Adstract) 



A series of species of Tropites and near relatives are exhibited, showing 

 evolution of the group and forming the basis for a discussion of species-form- 

 ing. These are species in the making and give good examples of series diverg- 

 ing but little from each other and from the common ancester. A discussion is 

 also given of the correlation of the Tropites suJ)'bullatus zone and the classi- 

 fication of the Upper Triassic of California. 



FAUNA OF THE IDAHO FORMATION 

 BY JOHN C. MEERIAM 



(A'bstract) 



A very extensive series of sediments exposed in the valley of the Snake 

 River, in southwestern Idaho, described by Cope as the Idaho formation, has 

 been carefully studied and described by Lindgren. From this formation a 

 mammalian fauna secured by Lindgren has been listed by Lucas and referred 

 to the Pliocene. 



The known list of mammals from the Idaho includes a number of forms 

 which approach very closely in their stage of evolution to the Pleistocene of 

 western North America, but differ specifically from all Pleistocene species. 

 fSuch differences as appear are mainly in the direction of primitiveness. A 

 number of other forms found in the Idaho fauna are distinctly of a Pliocene 

 type. As nearly as can be judged, the mammalian fauna of the Idaho repre- 

 sents a Pliocene stage later than any other Pliocene fauna of the Pacific Coast 

 and Great Basin regions, with possible exception of the Tulare Pliocene oc- 

 currence on the western border of the San Joaquin Valley. 



OCCURRENCE OF A MARINE MIDDLE TERTIARY FAUNA ON THE WESTERN 

 BORDER OF THE MOJAVE DESERT AREA 



BY WALLACE GORDON 



Read by J. C. Merriam. 



