INTRODUCTION In 1940 Leene published Part I of the Snellius portunids, with the stated intention of using the remaining material to produce monographs of the genera Thalamita and Neptunus (now Portunus). These monographs did not eventuate and at the invitation of Dr. L. B. Holthuis the material was made available for study by the author at the Rijksmuseum van Natuurlijke Historie in Leiden. The original intention was to report upon the collections of the Snellius expedition and upon the accrued specimens from the Indo-West Pacific area in the Leiden Museum which belonged to described species. It was then intended to publish separately upon the undescribed species in these and other collections. Instead these undescribed species are included...