Introduction This is the second volume of a series dealing with neotropical Notodontidae. A previous publication in Vol. 4 of this series, “An illustrated Type Catalogue of the Notodontidae in the National Museum of Natural History, Washington, D.C.” (Schintlmeister, 2016) clarified the identity of many neotropical notodontids by designating 733 lectotypes, which were described primarily by Schaus 1889 - 1939 and Dognin 1889 - 1924. The present publication deals with the genus Hemiceras Guen.e, 1852, which has gained a poor reputation as a taxonomically difficult group. Draudt (1933) wrote in the German edition of Seitz: “Eine ganz ungeheuer gro.e Gattung sehr einheitlicher, einander vielfach .u.erst .hnlicher und schwierig auseinander zu haltender Arten ...” [A monstrous large genus of very uniform species, often extremely similar to one another and difficult to separate]. The last comprehensive description of American Notodontidae by Draudt (1932-1933) in Seitz contains 167 species (including 2 species in the genus Schausiades), with 88 species illustrated. A checklist of neotropical Notodontidae by Becker (2014) lists 201 species in the genus Hemiceras. Fifty-six taxa are newly synonymized. Seven lectotypes and one neotype designations stabilize the nomenclature by fixing the identity of these species. Out of 210 species, currently treated as valid, 51 are newly described, as are ten subspecies. The high percentage of newly described species in this revision shows the limitation our current knowledge of neotropical Notodontidae. Material and Methods This work is based on survey of all known primary types and also on examinations of their genitalia, should dissections have been made by earlier researchers. Only a very few primary types (cadmia Guen.e, 1852, sabis Guen.e, 1852, meona Cramer, 1781, jacksoni Kaye, 1925 and postica Maassen, 1890) could not be located. More than 30,000 adults and about 1700 genitalia slides of Hemiceras from various museums, institutions and private collections have been examined for this study. Adults where photographed using portable equipment with a circular full-spectrum tube of 5500 K and 22W power light source. The background was neutral grey, 40% black. In taking the images a Panasonic Lumix FZ150 digital camera was used. Color plates with adults were compiled with Adobe Photoshop from individual photographs in different layers. To knock out the background of the individual photos masking was used. Adults on the plates are illustrated in actual size (scale 1:1). Due to the subtle differences in forewing pattern of adults one male of each species was illustrated enlarged (scale 1.8 :1). Most genitalia illustrated here were mounted by Tibor Csövarie and Nikolai Ignatiev in accordance with the NHMUK-standard and embedded in Euparal. For photographing the slides a MNA43000 Camera attached to a Nikon SMZ 1500 Microscope was used. More than 500 genitalia slides from USNM has been mostly mounted by M. Pogue and were photographed by the author with an Apple iPhone 8. This technique have been described in Schintlmeister (2014). All genitalia slides have been photographed with a scale bar. To enhance the quality of these images, they were processed (unsharp masking, tonal adjustments and others) using Adobe Photoshop. The photos were then transferred onto grey-scaled images. Type localities were cited as given in the original descriptions including misspelled localities. If no country was provided in the original type locality it was added in square brackets. Also, geographical coordinates have been added in square brackets to each type locality if it was located by the author. Nomenclatural and taxonomical details with references such as the designation of a lectotype or synonymies are provided if these changes have not been included in the catalogue of Notodontidae (Schintlmeister 2013). The legends on the color plates and the genitalia plates follow principally to the labels on the adults, but country is given in English. Misspellings have been corrected and the collector was uniformly denoted by “leg.” In case of Vitor O. Becker, his spellings on the labels “V.O. Becker Col.” have been taken over. Distribution maps are based on the data of individual adults, all of which have been checked by the author and mapped using dots. Type locality of the species is marked on the maps by a five pointed star; type localities of other taxa of the same species (synonyms or subspecies) using a different star-symbol with explanation of the taxon-name. If the geographic indication on the data label of the voucher was too general or the location noted was not found, no point was set.