4. The presence or absence of teeth in the upper and lower jaws. This is indicated by a formula in which 0 means absence of teeth; max. means presence of teeth in the upper jaw; mand. means presence of teeth in the lower jaw. 5. The terminal joints or phalanges of the fingers and toes are sometimes _claw-shaped_. See p. 26. 6. The shape of the centra of the vertebrae.–_Opisthocoelous_, if the posterior end is cup-shaped or concave, _procoelous_ if the anterior end is concave and the posterior is convex. See p. 19. By means of these characters we can arrange the Anura in the following key:– I. Aglossa. Sacral diapophyses dilated. } AGLOSSA, p. 143. {139} Vertebrae opisthocoelous, with ribs. } II. Phaneroglossa. _A_. Arcifera. _a_. Sacral diapophyses dilated. α. Terminal phalanges not claw-shaped. Opisthocoelous, with ribs, max./0 } DISCOGLOSSIDAE, p. 152. Procoelous, without ribs, 0/0 } BUFONIDAE, p. 166. Precocious, or opisthocoelous,} without ribs, max./0 } PELOBATIDAE, p. 160. β. Terminal phalanges claw-shaped–HYLIDAE { max./mand. _Amphignathodontinae_, { p. 188. { max./0 _Hylinae_, p. 189. _b_. Sacral diapophyses cylindrical–CYSTIGNATHIDAE { max./mand. _Hemiphractinae_, { p. 210. { max./0 _Cystignathinae_, p. 211. { 0/0 _Dendrophryniscinae_, p. 227. _B_. Firmisternia. _a_. Sacral diapophyses dilated–ENGYSTOMATIDAE { max./0 _Dyscophinae_, p. 235. { 0/mand. _Genyophryninae_, p. 236. { 0/0 _Engystomatinae_, p. 225. _b_. Sacral diapophyses cylindrical–RANIDAE { max./mand. _Ceratobatrachinae_, { p. 237. { max./0 _Raninae_, p. 238. { 0/0 _Dendrobatinae_, p. 272. Concerning the evolution of the classification of the Anura, it is interesting to follow the changes of the value attached to the various anatomical characters by systematists. At first the presence or absence of teeth and of adhesive discs on the fingers and toes were considered to be of prime importance for the division of the Phaneroglossa. Duméril et Bibron, 1841. "Erpétologie générale." I. PHRYNAGLOSSES = Aglossa of Wagler: _Pipa_ and _Xenopus_. II. PHANÉROGLOSSES. 1. With teeth. _a_. Without discs: Raniformes. _b_. With discs: Hylaeformes.