Chaetetes, a fossil demosponge, is the common reef-building organism of the Carboniferous. As such, Chaetetes commonly occurs as laminar, domical, or columnar colonies. As is true of a number of clonal reef-builders, the growth form has been considered a reflection of the depositional environment with columnar colonies indicating greater turbulence. Such is not unreasonable, but it is possible that the different growth forms are different species. Variations in the microstructural details of chaetetid colonies has been used to distinguish species of Carboniferous Chaetetes. Unfortunately, these features are subject to diagenetic alteration and the degree of variability within these features is great. Characteristics of nearly all the "species" of Carboniferous Chaetetes can be found on a polished surface of a single specimen. Proposed research will: 1) test the validity of the criteria used to distinguish species of Carboniferous Chaetetes of North America; 2) look for criteria that might be less affected by preservation and more indicative of genetic variability, such as the way new calicles are added to the colony; and 3) determine the degree to which the growth form of chaetetid species is environmentally controlled. By clarifying the taxonomy of chaetetids it will be possible to address: 1) anomalies in the spatial and temporal distribution of this group, 2) some aspects of Carboniferous extinction events, and 3) the role of chaetetids in the structure and development of Carboniferous reefs.