Specimens (4): ♂, 40771, testis 9 × 6 mm., 51.0 gm. (July 9), 5 km. S Champotón; ♀, 40770, ovary moderately active (ova to 2 mm.), brood patch, 42 gm., moderate fat (August 9), 3½ km. N San Miguel, Isla Cozumel; ♀, 40768, imm., 45.2 gm., moderate fat (August 18), 2 km. WSW Sisal; ♂, 40769, testis 10 × 5 mm., 51.8 gm. (August 9), 13 km. WSW Sisal. Mallophaga: Myrsidea sp., July 9.
Toxostoma guttatum (Ridgway): Cozumel Thrasher.—Our specimen had enlarged testes and seems to represent the first record of breeding activity in the species.
Specimen (1): ♂, 40772, testis 7 × 4 mm., 49.5 gm. (August 10), 3½ km. N San Miguel, Isla Cozumel.
Turdus grayi Bonaparte: Clay-colored Robin.—Four adults were in full breeding condition.
Specimens (6): ♂, 40780, testis 13 × 8 mm., brood patch (July 10), 5 km. S Champotón; ♀, 40781, ova to 8 mm., 79.6 gm. (July 15), 5 km. SW Escárcega; ♀, 40776, 61.3 gm. (July 21), Pisté; ♀, 40777, imm., 63.4 gm. (July 20), 6½ km. W Pisté; ♂, 40779, testis 14 × 8 mm., brood patch, 68.5 gm. (July 30), and ♂, 40778, testis 13 × 11 mm., 71.5 gm. (July 28), Pueblo Nuevo X-can.
Polioptila caerulea (Linnaeus): Blue-gray Gnatcatcher.—A fledgling taken at Pisté was barely flying with remiges and rectrices ensheathed basally. Previous breeding records are for April 11 and 27 (Paynter, 1955a:231). A male taken on August 10 on Isla Cozumel had nearly completed molting into winter plumage.
Specimens (8): ♀, 40788, fledgling, 5.0 gm. (July 20), 6½ km. W Pisté; ♂, 40787, testis 2 × 1 mm., 5.6 gm. (July 21), ♂, 40785, juv., 5.8 gm. (July 22), and ♀, 40786, 5.6 gm. (July 22), Pisté; ♀, 40791, juv., 5.6 gm. (August 8), ♂, 40790, juv., 5.8 gm. (August 8), ♀, 40789, 5.7 gm. (August 9), and ♂, 40792, 5.3 gm., molting—7th primaries ensheathed (August 10), from {2½}-{3½} km. N San Miguel, Isla Cozumel.
Polioptila albiloris Lawrence: White-lored Gnatcatcher.—This species was abundant in the arid scrub along the coast in the vicinity of Sisal.
Specimens (2): ♂, 40783, testis 1 mm., 6.2 gm. (August 7), 1½ mi. S Sisal; ♂, 40784, testis 1 mm., 5.8 gm. starting to molt—1st and 2nd primaries ensheathed (August 10), 13 km. WSW Sisal.
Ramphocaenus rufiventris (Bonaparte): Long-billed Gnatwren.—Specimen (1): ♀, 40793, imm. skull, 9.8 gm. (July 15), 7½ km. W Escárcega.