Halfmoon Tail Betta

The Half Moon is a very desirable tail type. It is characterised by having the full 180 degree spread when flared, forming a "D" shape with straight edging. Dorsal and anal fins are also dramatically larger than those on other fin types. HMs are prone to tail-biting and fin damage, their tails are large and unnatural and HMs often feel hampered down by their fins. This also means they're one of the hardest tail types to breed as the males find it hard to successfully wrap the females.

(Taken from here)