Specimens (2): [Female], 40424, ovary 9 × 3 mm., 41.5 gm. (August 8), and [Male], 40423, testis 6 mm., 40.0 gm. (August 11), Isla Cozumel. _Porphyrula nartinica_ (Linnaeus): Purple Gallinule.--A female was taken in the tall grass where red rails were found on Isla Cozumel. Specimen (1): [Female], 4025, ovary 14 x 7 mm., 169 gm. (August 10), 3-1/2 km. N San Miguel. _Haematopus ostralegus_ Linnaeus: Oyster-catcher.--Two individuals were seen along the beach about 6 km. W Sisal on August 10 and 11. _Charadrius alexandrinus tenuirostris_ (Lawrence): Snowy Plover.--This was one of the commonest shorebirds on the beaches and mudflats west of Sisal. Several immature birds were taken, along with a pair of half-grown chicks, indicating the species was breeding, or recently had bred, there. No previous record of this species breeding on the peninsula has been found. Specimens (6): [Female], 40431, ovary inactive, 38.2 gm. (August 7), 4 mi. S Sisal; [Male], 40426 testis minute, 35.4 gm. (August 9), [Female], 40427, half-grown chick, 25.4 gm. (August 9), [Male], 40428, half-grown chick, 21.2 gm. (August 9), [Female], 40430, imm., 38.0 gm., little fat (August 10), [Female], 40429, ovary inactive, 35.7 gm., little fat, molting--1st through 6th primaries and middle pair of rectrices are new (August 10), all from 13 km. WSW Sisal. Mallophaga: _Actornithophilus ochraceus_, August 9; _Quadraceps assimilis major_, August 7. _Charadrius wilsonia wilsonia_ Ord: Wilson Plover.--A flock of about 11 was seen on the beach north of the village on Isla Mujeres on August 1. Two specimens were collected on the leeward side of the island about three kilometers south of the village on August 2. The only evidence of breeding was slightly enlarged testes in one male. Two individuals were sighted on the east coast of the mainland at Puerto Juarez on August 4. The species was common 3 to 13 km. west-southwest of Sisal; specimens taken there may have been migrants. Specimens (5): [Male], 40435, testis 3 × 1 mm., 59.0 gm. (August 2), and [Female], 40436, ovary inactive, 49.3 gm. (August 2), Isla Mujeres; [Female], 40434, ovary inactive, 53.6 gm. (August 7), [Male], 40433, testis 1 mm., 54.5 gm. (August 9), and [Male], 40432, imm., 53.7 gm., little fat (August 11), 3-13 km. WSW Sisal. Mallophaga: _Quadraceps assimilis major_, August 2 and August 11. _Actitis macularia_ (Linnaeus): Spotted Sandpiper.--A total of six individuals was seen on Isla Mujeres; each was alone. The species was common at Sisal where it was often seen in small mixed flocks with Snowy Plovers and Wilson Plovers. Specimens (3): [Male], 40437, testis 2 × 1 mm., 33.8 gm. (August 9), [Male], 40438, imm., 28.2 gm. (August 10), and sex? 40439, imm., 31.0 gm. (August 10), 13 km. WSW Sisal. Mallophaga: _Quadraceps ravus_; August 10.