ArticlesSpecial Article THE CLASSIFICATION OF THE OPALINIDÆ By Maynard M. Metcalf See allHide authors and affiliations Science 06 Aug 1920:Vol. 52, Issue 1336, pp. 135-136DOI: 10.1126/science.52.1336.135 Maynard M. Metcalf Find this author on Google Scholar Find this author on PubMed Search for this author on this site Article Info & Metrics eLetters PDF This is a PDF-only article. The first page of the PDF of this article appears above.