
The major part of this study was carried out at the University of Kansas in 1946–48 under the direction of Dr. R. H. Beamer, as a thesis problem for the Master of Arts degree. At the University of Michigan in 1953–54, with the assistance of Dr. T. H. Hubbell, some uncertain points were cleared up and the manuscript was brought up to date and prepared for publication. Examination was made of 2,283 specimens of the seven species and one subspecies of the genus.
| selected citations These citations are derived from selected sources. This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | 2 | |
| popularity This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network. | Average | |
| influence This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | Top 10% | |
| impulse This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network. | Average |
