Order III. ANURA or TAILLESS AMPHIBIA.
The recent tailless Amphibia, or Frogs and Toads in the widest sense, contain such a great number of species (about 900), with such a diversity of characters, that it is necessary, if only for the sake of mere convenience, to group them into a considerable number of families and sub-families. The characters available for this purpose are few.
1. The possession of a tongue characterises the Phaneroglossa, the absence of a tongue the Aglossa.
2. The character of the shoulder-girdle.–Overlapping of the two halves of the shoulder-girdle on the ventral side characterises the Arcifera, while in the Firmisternia the two ventral halves meet in the middle line and form a firm, median bar. See, for details, p. [24].
3. The shape of the transverse processes or diapophyses of the sacral vertebra which carries the iliac or hip-bones. These processes are either dilated or cylindrical.
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:–
| II. Aglossa. Sacral diapophyses dilated. |  | AGLOSSA, p. [143]. |
| 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– |  | max./mand. Amphignathodontinae, p. [188]. |
| HYLIDAE | max./0 Hylinae, p. [189]. | |
| b. Sacral diapophyses cylindrical– |  | max./mand. Hemiphractinae, p. [210]. max./0 Cystignathinae, p. [211]. 0/0 Dendrophryniscinae, p. [227]. |
| CYSTIGNATHIDAE | ||
| B. Firmisternia. | ||
| a. Sacral diapophyses dilated– | | max./0 Dyscophinae, p. [235]. 0/mand. Genyophryninae, p. [236]. 0/0 Engystomatinae, p. [225]. |
| ENGYSTOMATIDAE | ||
| b. Sacral diapophyses cylindrical– | | max./mand. Ceratobatrachinae, p. [237]. max./0 Raninae, p. [238]. 0/0 Dendrobatinae, p. [272]. |
| RANIDAE | ||