Two species of the red algae genus Cottoniella, C. filamentosa and C. fusiformis, are reported for the first time from North Carolina, USA. A vegetative structure that includes four pericentral cells and two flanking cells that are cut off from the lateral pericentral cells is characteristic of both species. The two species are distinguished by the number of monosiphonous filaments that develop on each segment with C. filamentosa having one and C. fusiformis having two. Development of tetrasporangia in C. fusiformis also was observed for the first time and found to follow a similar pattern to that reported for C. filamentosa except that adaxial cover cells may cut off additional corticating cells in this species. No specimens of Cottoniella were found during extensive surveys of North Carolina's offshore algal flora in the 1970s and many additional collections made from 2004 to 2007. Both species have been found in collections from four sites since August 2007 and it is believed that these represent a northern range expansion along the United States east coast. The previous United States distribution limit for C. filamentosa was the Florida Keys, 1300 km south from North Carolina and this is the first report of C. fusiformis in the United States.