Abstract
About 195 species of theridiid spiders are known from north of Mexico, about 800 in all the Americas. Among them are our commonest spiders but also numerous rare species. This is the first addition to my revisions of spiders of this family. Similar additions will be made periodically as it becomes necessary to report on new species, describe the other sex of species known from only males or females, record habitat notes of rare species and make corrections.For their assistance I want to thank Miss M. E. Galiano of Buenos Aires, Mr. V. D. Roth of the Southwestern Research Station of the American Museum of Natural History, who collected specimens of rare Arizona species, and Dr. W. J. Gertsch, who made me aware of an error in my revision of the genus Tidarren and facilitated the loan of Latrodectus mactans hesperus. This research is in part supported by Public Health Research Grant AI-01944 from the National Institute of Allergy and Infectious Diseases.