MPEP 2163.03(V) states "An original claim may lack written description support when ... (2) a broad genus claim is presented but the disclosure only describes a narrow species with no evidence that the genus is contemplated. See Ariad Pharms., Inc. v. Eli Lilly & Co., 598 F.3d 1336, 1349-50 (Fed. Cir. 2010) (en banc)."
Here, the use of the singular in "a narrow species" could suggest that this rejection is only allowed if one species is disclosed, and that this rejection is prohibited if two species are disclosed. However, the cited decision is explicit that this is not the case. "Nor do we set out any bright-line rules governing, for example, the number of species that must be disclosed to describe a genus claim, as this number necessarily changes with each invention, and it changes with progress in a field." Ariad Pharmaceuticals, Inc. v. Eli Lilly and Co., 598 F. 3d 1336, 1351 (Fed. Cir. 2010).