660 



SCIENCE 



[N. S. Vol. XLII. No. 1088 



a short-faced tiear resembling Arctothermm, of 

 the American Pleistocene, while the north polar 

 regions are inhabited by the polar bear, Thal- 

 arctos. The ancestry of the bears is still clouded, 

 none being known below the Pliocene. 



Systematically the bears are a compact group, 

 yet within the genus TJrsus several subgroups may be 

 recognized; the subgenus Euarctos, containing the 

 black or cinnamon bears and the subgenus Ursits, 

 containing the grizzly and brown bears. Of the 

 latter (grizzly and brown bears) two, three and 

 even four species, representing different species- 

 assemblages, may be found in a single locality, as 

 in the fossil deposits of Raneho La Brea or in 

 Yellowstone National Park. The characters used 

 in identification are chiefly cranial and dental. 

 Skulls of males of the grizzly group are two, and 

 in some cases, three times the bulk of those of 

 females of the same species. At present about 40 

 species of grizzlies and 10 of brown bears are 

 recognized, where formerly but one of each was 

 known. For example, California once contained 

 representatives of five different groups of grizzlies. 

 The recognition of this large number of species 

 has been made possible by the extensive collections 

 of skulls in the United States National Museum 

 and in the California Museum of Vertebrate Zool- 

 ogy. 



Fossil Tertiary Mollusca of the BocJcy Mountain 

 Segion: T. D. A. Cockerell, University of Col- 

 orado, Boulder, Colorado. 



The recent expeditions of the American Museum 

 of Natural History, primarily for the discovery of 

 mammalian remains, have brought to light some 

 very interesting Tertiary land and freshwater 

 shells, principally in Wyoming and New Mexico. 

 From a study of these we are led to the following 

 conclusions : 



1. Certain of the most characteristic genera of 

 the Rocky Mountain land shells living to-day are 

 apparently very ancient inhabitants of the same 

 general region, and have, perhaps, at no time ex- 

 tended very much beyond it. The most note- 

 worthy example is Oreohelix, represented in the 

 Eocene and Paleocene by large species, some of 

 the specimens showing the sculpture of the apical 

 whorls, which agrees with that of the group 

 called Sadiocentrum by Pilsbry. A species of 

 Eolospira from the New Mexico Paleocene is ex- 

 tremely like a living species of Arizona. 



2. Ashmunella, one of the most characteristic 

 endemic genera of the southwest, is not at present 

 known below the Pleistocene. It is not possible 

 to be sure, at present, whether all the peculiar 



genera of the Eooky Mountain region and south- 

 west are very ancient inhabitants of that country, 

 but it seems very likely that they will all be found, 

 sooner or later, in the early tertiaries. 



3. Various circumpolar genera of small snails, 

 such as Pupilla and Cochlicopa, represented in the 

 modern fauna by species identical or nearly iden- 

 tical with those of Europe and northern Asia, are 

 apparently lacking in the Tertiary, or at any rate 

 in the Eocene. They may have been overlooked, 

 but it is probable that they have reached our re- 

 gion in much more recent times, from Eurasia, as 

 their small amount of modification, or total lack 

 of it, would suggest the Eocene collections do con- 

 tain small species of more characteristically 

 American types as Vitrea and Thysanophora. 



4. The Paleocene and Eocene faunas included a 

 series of genera entirely different from anything 

 now living in the same region, but evidently re- 

 lated, at least in part, to the present Central Amer- 

 ican and West Indian faunas. Thus we have from 

 the Eocene of Wyoming species apparently refer- 

 able to Pleurodonte and Eucalodium. It is not 

 clear, at the present time, whether this Central 

 American fauna originated northward, or whether 

 it had its main center in the region where it now 

 exists, merely extending northward during a time 

 when the country now represented by Wyoming 

 and Colorado was low, moist and warm. 



5. The most remarkable discoveries have been 

 of small shells belonging to the Bulimulidae, hav- 

 ing the aperture or last whorl upturned, repre- 

 senting at least two genera (Protoioysia and 

 Grangerella) and four species. These, while be- 

 longing to extinct genera, show evident relation- 

 ship with some of the South American snails, and 

 at the same time a remarkable resemblance to the 

 Indian genus Boysia, which is supposed to belong 

 to the Pupillida, though the anatomy is unknown. 



6. Among the fresh-water shells, the Unionidse 

 are the most interesting. About the end of the 

 Cretaceous and beginning of the Tertiary we find 

 in the Eocky Mountain region a large and varied 

 series, resembling the types which now inhabit the 

 Mississippi Valley. At about the same time that 

 the dinosaurs disappeared, these mussels also de- 

 parted, leaving an impoverished Unionid fauna in 

 the Eocene, which in its turn eventually died out 

 altogether. It seems probable that this change was 

 connected with earth movements. 



Isolation as a Factor m the Evolution of Thais 

 lamellosa (illustrated with specimens and lan- 

 tern slides) : Trevor Kincaid, University of 

 Washington. 



