Abstract
Cyclotella alchichicana sp. nov. is described from Lake Alchichica, Puebla, Mexico, a saline and alkaline crater-lake in Central Mexico. The new species is similar to C. quillensis from which it distinguished by the arrangement of the marginal fultoportulae and by the external opening of the rimoportula that is elongated slit-like and lacking the external projection on the mantle. Some habitat and ecological data where C. alchichicana has been observed are provided.