This paper contains the diagnoses of 11 new Species and of 2 new Varieties, all belonging to the genus Alpheus Fabr. The Macrura, collected by the „Siboga-Expedition”, are at present at Ierseke, but will be transferred to the Zoological Museum of the University of Amsterdam, as soon as they have been worked out. 1. Alpheus Hailstonei Cout., var. laetabilis, n.