1 Of or in or belonging to the cavity of the abdomen (US spelling) (6)
4 The ---, female vocal trio comprising Diana Ross, Mary Wilson and Florence Ballard (8)
8 Invest with ministerial or priestly authority (6)
9 Author and creator of the character Dr. Finlay (1,1, 6)
10 London street; croquet-like game (4,4)
11 Wine from the Jerez region of southern Spain (6)
12 Fish; atomic submarine in a children's programme - captained by Troy Tempest (8)
13 Sean ---, Irish author of Juno and the Paycock (1924) (1'5)
15 Pandemonium, an uproar (6)
18 Capital of South Australia (8)
20 A plane curve traced by a point circling about the centre but at ever-greater distances from it (6)
21 Play by Aristophanes, c 405 BC (3,5)
23 Or The Peer and the Peri, operetta by Gilbert and Suillivan (8)
24 Town near Dounreay (6)
25 Sea-nymphs in Greek mythology (8)
26 Greek goddess of wisdom, etc. (6)

1 Children's disease; the rump of a horse (5)
2 US Open tennis champion 1985-7 (4,5)
3 A mythical being that is half man and half horse (7)
4 European Footballer of the Year, 1956 (7,8)
5 Pablo, cubist painter (7)
6 Sacred words or syllables repeated in prayer or meditation (7)
7 Winner of the 1985 British Open (5,4)
12 --- Coe, winner of the 1980 and 1984 Olympic 1,500 metres races (9)
14 Partick Thistle and Scotland goalkeeper (4,5)
16 One of the first petrol-driven cars to be marketed, named for its German inventor, Gottlieb (7)
17 Swindled; fined (7)
19 Sister of Orestes who murders her mother (7)
22 Trademark for a brand of fine English porcelain (5)