living in isolated populations
on the higher mountains in Mexico, probably will be of great
significance in understanding dispersal and differentiation of animals
during the Pleistocene.

SPECIES OF QUESTIONABLE OCCURRENCE

Some species for which there are no authentic records from Michoacan can
be expected there on zoogeographic probability. Other species have been
recorded from Michoacan, but these records are doubtful for any one of
several reasons. Fifteen species of such questionable occurrence are
discussed below:

~Syrrhophus modestus modestus~ Taylor

_Syrrhophus modestus_ Taylor, Univ. Kansas Sci. Bull.,
28:304, May 15, 1942.--Hacienda Paso del Rio, Colima,
Mexico.

_Syrrhophus modestus modestus_, Duellman, Occ. Pap. Mus.
Zool. Univ. Michigan, 594:5, June 6, 1958.

This small terrestrial frog is not uncommon on the coastal lowlands and
foothills in Nayarit and in Colima, where it has been collected within a
few kilometers of the Michoacan border. At Tecolapa, Colima, on August
9, 1956, _Syrrhophus modestus modestus_ was found with _Tomodactylus
nitidus orarius_, _Bufo marinus_, _Bufo marmoreus_, _Hyla baudini_,
_Hyla smithi_, and _Phyllomedusa dacnicolor_, all of which occur on the
coastal lowlands of Michoacan. Because of its solitary and secretive
habits, _Syrrhophus modestus modestus_ is not common in collections.
Additional field work on the coast of Michoacan should reveal the
presence of the species there.

~Hyla microcephala sartori~ Smith

_Hyla microcephala sartori_ Smith, Herpetologica, 7:186,
December 31, 1951.--1 mi. N of Organos, S of El Triente,
Guerrero, Mexico.

On August 28, 1960, J. R. Dixon obtained a series of this species from a
temporary pond 6 kilometers northeast of La Resolana, Jalisco.
Previously, _Hyla microcephala sartori_ had been known only from the
lowlands of Guerrero and Oaxaca. The existence of the species in Jalisco
provides evidence that this frog also occurs in Michoacan and Colima.

~Gastrophryne usta usta~ (Cope)

_Engystoma ustum_ Cope, Proc. Acad. Nat. Sci. Philadelphia,
18:131, 1866.--Guadalajara, Jalisco, Mexico.

_Gastrophryne usta usta_, Carvalho, Occ. Pap. Mus. Zool.
Univ. Michigan, 555:13, July 16, 1954.

Smith and Taylor (1948:93-4) listed specimens of this species from
Organos and El Treinta, Guerrero, and from Paso del Rio, Queseria,
Santiago, and Tecoman, Colima. The spe