Despite the fact that taxonomically the name Eurypelma californicum (Ausserer 1871) has been regarded as a nomen dubium and thus invalid for several decades, it is increasingly used in non-taxonomic publications and on the internet. This makes it necessary to trace back the identity of the spiders involved. The taxonomy of Eurypelma californicum and Aphonopelma hentzi (Girard 1852) was investigated, and it is concluded that the spiders referred to as Eurypelma californicum in physiological publications of the last 35 years belong to an Aphonopelma species, most likely A. hentzi.