Complex sentence: The two river martin species are usually considered to belong to a single genus, "Pseudochelidon" due to their having a number of structural similarities, but Brooke proposed that the White-eyed River Martin be placed in a separate monotypic genus "Eurochelidon".
Split into simpler sentences: The two river martin species are usually considered to belong to a single genus, "Pseudochelidon", due to their having a number of structural similarities. However, Brooke proposed that the White-eyed River Martin be placed in a separate monotypic genus "Eurochelidon".