In this family Oates retained only the one genus, Regulus, whilst he placed Leptopaecile and Cephalopyrus in his subfamily Liotrichinae of the family Timaliidae. Gadow, in Volume viii. of the British Museum Catalogue of Birds places the first two genera in the Regulidae, whilst Cephalopyrus he keeps with the Titmouses, Paridae, in the genus Aegithalus. Hartert, on the other hand, places all three genera in the Paridae, though he does not absorb Cephalopyrus into AEgithalus or into any of the other genera.
I can see no resemblances to the Timaliidae in either Regulus or Leptopaecile, which are undoubtedly very closely allied. Cephalopyrus is very close to Leptopaecile but differs from both the other-genera in its most unusual Nidification. With the Warblers they have many characters in common and, probably, their most correct position would be between the Paridae and Sylviidae.
In this family, Regulidae, the birds are all alike very small with thick soft plumage: the head is sub-crested ; the bill is small and straight, less than half the length of the head: rictal bristles are present, though in different degree and there is an operculum, or semi-operculum, over the nostril, which is placed in a groove ; the wing is short and rounded, the 4th, 5th and 6th primaries being subequal; the tail is shorter than the wing but varies in shape; the tarsus is long, more than two and a half times the length of the hind toe without claw.
Key to Genera.
A. Nostrils covered with a stiff feather ………..Regulus, p. 538
B. No feather over nostril.
a. Crown chestnut suffused with blue ; tail
well rounded Leptopaecile, p. 542.
b. Crown orange-red; tail square……….Cephalopyrus, p. 544.