It is a test for comparing median lethal concentration values. the reference paper is Wheeler et al. 2006 (Environmental Toxicology and Chemistry 25: 1441-1444). Thank you!
If I may put my two cents in, you could try the "comped" function implemented in the R-package "drc" (Ritz and Streibig, 2005). Maybe not the one you are looking for but it does its job. Check the link for further information.