- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
"The neontological concept of a species as a group of 'unit populations' divided into geographical races or subspecies is applied to the palaeontological record, and the intrinsic similarities of geographical and chronological subspecies are discussed. It is concluded that the variety and the subspecies are different entities both of which have value in palaeontology. Quantitative measures of the level of specific and subspecific distinction are proposed."