| Its eastern limit in Russia is hard to define, due to extensive hybridisation and intergradation with the Siberian spruce, but is usually given as the Ural Mountains. |
| Specimens from a transect of southeastern Sonora show intergradation between Perognathus goldmani and P. artus. |
| He called for deeper intergradation to achieve more unified GCC accomplishments. |
| No evidence of intergradation with any other race was noted. |
| Whether actual intergradation ever takes place across the narrow Bering Strait I do not know. |
| The extensive intergradation that has resulted from interbreeding is the chief cause of classification difficulties. |
