THE AMERICAN SPECIES OF EUBOSMINA SELIGO (CRUSTACEA, CLADOCERA)

Eubosmina is represented in the Americas by at least four species, of which two, E. coregoni (Baird) and E. longispina (Leydig), are Holaretic; E. hagmanni (Stingelin) and E. tubicen (Brehm) appear to be strictly Neotropical. Eubosmina coregoni, which lacks a mucro, has rarely been reported from North America, but now appears to be common in the Great Lakes. Eubosmina longispina, with ventral incisures on the mucro, is familiar as a late‐ and postglacial fossil in the eastern U.S. and is the common bosminid today in northern New England and eastern Canada. The two American endemics, both with dorsal incisures on the mucro, occur widely from Argentina to southern Canada; the more widespread, E. hagmanni, is known from Tierra del Fuego and may occur in the Canadian Arctic. The two can be difficult to separate unless males are present, as they rarely are. In typical summer populations, however, the female rostrum shows positive allometry in E. hagmanni but negative allometry in E. tubicen; the mucro shows zero or weakly negative allometry in E. hagmanni but positive allometry in E. tubicen. In no known locality do these two species occur together, but in a few New England and Canadian lakes, where E. longispina is present, populations that otherwise resemble E. tubicen show negative allometry of the mucro. This situation is provisionally attributed to character displacement.