FIGS. 11, 12.--MEDIAL VIEW OF LOWER JAWS OF TWO SHREWS 30 FIGS. 13, 14.--SECOND UNICUSPID TEETH OF SHREWS 30 FIG. 15.--DIAGRAM OF PROBABLE PHYLOGENY OF SHREWS 32 FIGS. 16-18.--GEOGRAPHIC DISTRIBUTION OF SUBSPECIES 33-40-53 INTRODUCTION The purpose of this report is to make clear the biological relationships between the shrews of the _Sorex vagrans-obscurus_ "species group." This group as defined by H. H. T. Jackson (1928:101) included the species _Sorex vagrans_, _S. obscurus_, _S. pacificus_, _S. yaquinae_, and _S. durangae_. The last mentioned species has been shown (Findley, 1955:617) to belong to another species group. _Sorex milleri_, also assigned to this group by Jackson (1947:131), seems to have its affinities with the _cinereus_ group as will be explained beyond. The position of the _vagrans_ group in relationship to other members of the genus will be discussed. Of this group, the species that was named first was _Sorex vagrans_ Baird, 1858. Subsequently many other names were based on members of the group and these names were excellently organized by Jackson in his 1928 revision of the genus. Subsequent students of western mammals, nevertheless, have been puzzled by such problems as the relationship of (1) _Sorex vagrans monticola_ to _Sorex obscurus obscurus_ in the Rocky Mountains, (2) _Sorex pacificus_, _S. yaquinae_, and _S. obscurus_ to one another on the Pacific Coast, and (3) _S. o. obscurus_ to _S. v. amoenus_ in California. Few studies have been made of these relationships. Clothier (1950) studied _S. v. monticola_ and _S. o. obscurus_ in western Montana and concluded that the two supposed kinds actually were not separable in that area. Durrant (1952:33) was able to separate the two kinds in Utah as was Hall (1946:119, 122) in Nevada. Other mammalogists who worked within the range of the _vagrans-obscurus_ groups have avoided the problems in one way or another. Recently Rudd (1953) has examined the relationships of _S. vagrans_ to _S. ornatus_. MATERIALS METHODS AND ACKNOWLEDGMENTS Approximately 3,465 museum study skins and skulls were studied. Most of these were assembled at the University of Kansas Museum of Natural History, but some were examined in other institutions. Specimens were grouped by geographic origin, age, and sex. Studies of the role of age and sex in variation were made. Because it was discovered that secondary sexual variation was negligible, both males and females, if of like age and pelage, were used in comparisons designed to reveal geographic variation. External measurements used were total length, length of tail, and length of hind foot. After studying a number of cranial dimensions I chose those listed below as the most useful in showing differences in size and proportions of the skull. Figures 1 and 2 show the points between which those measurements were taken.