The Key to Scientific Names
(Apodidae; syn. Apus † Little Swift A. affinis) Gr. τετραγωνος tetragōnos square < τετρα- tetra- four- < τεσσαρες tessares four; γωνια gōnia angle; πυγη pugē rump; "The habit of placing the Little Swift (Cypselus affinis Gray) in the same genus as the European Swift (Micropus apus apus) and other fork-tailed species has long struck me as inconsistent. The Little Swift is the only species placed by systematists in the Micropus group which has a square instead of a truly forked tail, and although it conforms in other respects to the characters of that large genus, I consider that on account of that structural character it may be placed in another genus. As I find that there is no genus available for it, I propose the name Tetragonopyga, gen. nov. Type, Cypselus affinis Gray." (Bannerman 1932); "Tetragonopyga Bannerman, 1932, Bull. British Ornith. Club, LIII (ccclxiv), p. 72. Type, by original designation, Cypselus affinis J. Gray, 1830." (JAJ 2021).