. The biology of the amphibia. Amphibians. 494 THE BIOLOGY OF THE AMPHIBIA instrument for digging. Spade-foot Toads with their vertical pupil and smooth or slightly tubercular skins (Fig. 158) may be readily distinguished from the true toads, Bufo, which have a horizontal pupil and rough skin. Pelodytes, the third genus in the subfamily, lacks the "spade" of the other genera and is much slenderer and more froglike. It is known from two species, one in southwestern Europe and the other in the Caucasus. The Pelobatinae are closely allied. Scaphiopus with its cartilaginous sternum seems
. The biology of the amphibia. Amphibians. 494 THE BIOLOGY OF THE AMPHIBIA instrument for digging. Spade-foot Toads with their vertical pupil and smooth or slightly tubercular skins (Fig. 158) may be readily distinguished from the true toads, Bufo, which have a horizontal pupil and rough skin. Pelodytes, the third genus in the subfamily, lacks the "spade" of the other genera and is much slenderer and more froglike. It is known from two species, one in southwestern Europe and the other in the Caucasus. The Pelobatinae are closely allied. Scaphiopus with its cartilaginous sternum seems more primitive than either Pelo- bates or Pelodytes, which have bony sternums. On the other hand, Pelodytes with its free coccyx and Rana-like habitus seems less specialized than either Pelobates or Scaphiopus. The three genera are obviously closely allied (Boulenger, 1899; Noble, 1924), although it is difficult to state which stands nearest the ancestral stock from which they Fig. 158.—The eastern Spade-foot Toad, Scaphiopus holbrookii. The history of the Pelobatinae dates back to at least the Oli- gocene. Macropelobates is known from the Oligocene of Mon- golia. Pelobates and a closely allied genus have been described from the Lower Miocene of Europe. Other fossils, possibly identical with living species of Pelobates, have been reported from the Pleistocene of Germany. In brief, Spade-foot Toads were established in the Old World for the greater part of the Tertiary. Subfamily 3. Sooglossinae.—Pelobatids with a free coccyx, a horizontal pupil, and a ranid type of thigh musculature (the semitendinosus is separate from the sartorius and lies deep within the thigh musculature; its distal tendon passes dorsal to that of the gracilis major and minor). The three Seychelle Island frogs, Nesomantis thomasseti, Sooglossus sechellensis, and S. gardineri, have recently been shown to be pelobatids (Noble, 1926), although the first two have the external appearance of the rani
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