This volume conatins many articles written between 1919 and 1948. In the area covered, ten genera are recognized, one of them new. These genera include sixty sepcies, one variety, and two forms. Illustrations include drawings of microscopic detail. Originally published in 1951. A UNC Press Enduring Edition -- UNC Press Enduring Editions use the latest in digital technology to make available again books from our distinguished backlist that were previously out of print. These editions are published unaltered from the original, and are presented in affordable paperback formats, bringing readers both historical and cultural value.