296 PROCEEDINGS OF THE NATIONAL MUSEUM vol. ii4 



localized, and on or near the periphery of the range of the group or 

 section. 



Most of the United States, east of the 105th Meridian, is occupied 

 by at least two species of Camharincola, although as a rule the area 

 shared by any two given species is not extensive {mesochorea and 

 vitrea have the greatest territory in common). The number of species 

 tends to increase in certain regions — to five in the Ozark area and to 

 seven in southwest Virginia (the Pacific Northwest, still largely 

 unknown, must be omitted from consideration but it probably also 

 has a large number of species). 



Now the interesting inference to be drawn from known distributions 

 in the genus is that — in comparison with other members of theu* 

 respective subgeneric section — none of the species of the Appalachian 

 fauna can be considered as primitive, such forms rather occurring 

 in lowland regions where two or three widespread forms of Camharin- 

 cola are the dominant and often the only branchiobdellids. In 

 short, morphologically primitive species do not occur in the regions 

 having the richest branchiobdellid fauna at the present time. 



It will be recalled from a previous section (p. 290), that the general- 

 ized species of Camharincola represent to a considerable extent the 

 hypothetical form and structure of the familial archetype, and that 

 members of the Mesochorea section of the genus lack specializations 

 in virtually all of the major diagnostic characters. It is therefore 

 particularly significant that these species are, in a sense, now known 

 largely as relicts strung out along a highly probable route of migration 

 taken by cambarine cra3^fish in their occupation of eastern North 

 America. The two most prmiitive known species of the genus are 

 endemic to the Ozark region. A single species (holti) of the Macro- 

 cephala group occm^s in central Kentucky; its nearest relative in the 

 Columbia River system. The two species of the Branchiophila 

 group have essentially the same sort of transcontinental distribution. 



The distinctly more specialized Philadelphica group has its center 

 of abundance in the southern Appalachians where six species occur, 

 along with a variety of species of Pterodrilus and Xironodrilus. One 

 species of the Philadelphica group, macrodonta, occurs in the foothills 

 of the Rockies and in the adjacent High Plains, but it may be con- 

 tinuously linked up with the Appalachian fauna by way of Wisconsin 

 and Michigan (see map, fig. 57). Another species, chirocephala, 

 extends westward into the Ozarks and adjacent Great Plains. Two 

 other closely related species, osceola and vitrea, occur in the Great 

 Plains and southeastern Coastal Plain; they are both somewhat 

 primitive within the Philadelphica section. The true Appalachian 

 endemics {C. ingens, C. heterognatha, C. holostoma, and C. fallax, all 

 of the Philadelphica group, and the one known species of the Demissa 



