REVISION OF THE FISH FAMILY LIPARIDAE 27 



radiated. Some of the criteria ^ generally used in determining the 

 center of dispersal of a group point to one of these regions and some 

 to the other as the center of dispersal for the family. We shall not 

 attempt to decide between these two regions, but shall simply cite 

 the criteria which point to the northwest Pacific as the center from 

 which the existing groups have dispersed. 



1 . Most primitive species : This resolves itself into a discussion of 

 the center of dispersal of the most generalized genus Liparis. The 

 criteria utilized here, when applied to Liparis, indicate the North 

 Pacific as the place of origin of the genus. The primitive species of 

 Liparis are in the North Pacific. 



2. Greatest differentiation of type: Apparently all of the genera 

 originated in the North Pacific. Only three of the 13 genera are 

 found in any other region. The most generalized species of these 

 three genera exist in the North Pacific. It follows that the genera 

 are most closely related in this region. 



3. Giant species: The largest species of all the genera except 

 Paraliparis are found in the North Pacific. The specific attain the 

 greatest size about northern Japan. Those species which extend 

 from the American to the Asiatic coast attain the greatest size in the 

 latter region. The fact that the species attain the greatest size in 

 Asiatic waters does not necessarily indicate that this region represents 

 the center of origin. It may simply mean that the conditions here 

 are the most favorable for growth. 



4. Dominance or abundance of species: More than half of the 

 species exist in the Bering Sea and southward to Japan. Three- 

 fourths of the species are recorded from the North Pacific. 



5. Geographical consideration: We may readily account for the 

 present distribution of the family if we assume that the groups 

 dispersed from the North Pacific. The only barrier that we have to 

 contend with is the equatorial region. This effectively acts as a 

 barrier to the shallow-water species. We have already attempted an 

 explanation of the presence of tide-pool species in the Antarctic 

 region. We have assumed that the species were able to cross the 

 Equator during the glacial period. Whether or not this explanation 

 is satisfactory we must account for the crossing of the equatorial 

 region if we should assign to any other region the center of dispersal 

 for the family. 



6. Lines of convergence: In tracing out the lines of convergence 

 for a family we are concerned mainly with the genera. If all the 

 genera have originated in one region we are justified in designating 

 that region as the center of dispersal for the family. It is stated 

 under "Greatest differentiation of type" that aU the genera are 

 represented and probably arose in the North Pacific. 



• See C. 0. Adams, 1902, and A. Q. Ruthven, 1908. 



