Specimens (10): [Female], 40650, 42 gm., (July 10), 5 km. S Champotón; [Female], 40752, ovary inactive, 43.4 gm., molting--4th primaries ensheathed (July 14), and [Male], 40651, imm., 42.5 gm. (July 15), 6-7-1/2/# km. W Escárcega; [Female], 40645, ovary slightly enlarged (8 × 3 mm.), 47.5 gm. (July 21), [Female], 40643, ova to 1 mm., 39.3 gm. (July 21), [Male], 40644, testis 10 × 7 mm., 43.1 gm., starting to molt--1st primaries ensheathed (July 21), and [Female], 40646, imm., (July 26), Pisté; [Female], 40648, ova to 1 mm., 37.4 gm. (July 29), Pueblo Nuevo X-can; [Male], 40647, imm., 38.4 gm. (August 14), and [Female], 40649, 44.4 gm., molting--only outer 3 pairs of rectrices present and are ensheathed basally, 6th and 7th primaries ensheathed (August 15), 4 km. NNE Felipe Carrillo Puerto. _Myiodynastes luteiventris luteiventris_ Sclater: Sulfur-bellied Flycatcher.--The latest breeding record given by Paynter (1955a:191) is for the last week in June. A male taken on July 31 had enlarged testes. None of the following specimens was in the process of molt. Specimens (4): [Female], 40655, 44.5 gm. (July 10), 5 km. S Champotón; [Female], 40656, ovary slightly enlarged (8 × 4 mm.), 47.0 gm. (July 15), 7-1/2 km. W Escárcega; [Female], 40654, testis 10 × 4 mm., 39 gm. (July 31), Pueblo Nuevo X-can. _Megarhynchus pitangua mexicanus_ (Lafresnaye): Boat-billed Flycatcher.--I know of no previous breeding record for this species on the peninsula. The female obtained on July 25 was observed feeding young. Specimens (2): [Female], 40658, 57.6 gm. (July 11), 5 km. S Champotón; [Female], 40657, ovary 10 × 5 mm., 59.8 gm. (July 25), Cenote Seco, 2 km. E Chichén-Itzá. _Myiozetetes similis texensis_ (Giraud): Vermilion-crowned Flycatcher. --Paynter (1955a:192) reported this species breeding in mid-May. A male taken on July 17 west of Escárcega had enlarged (probably regressing) testes and indicates breeding later than May. Specimens (3): [Male], 40660, testis 6 × 3 mm., 32.0 gm. (July 17), and sex? 40661, 33.8 gm., molting--5th primaries ensheathed (July 17), 1 km. N, 13 km. W Escárcega; [Male], 40659, imm., testis 2 × 1 mm., 27.6 gm. (July 29), Pueblo Nuevo X-can. _Pitangus sulphuratus guatimalensis_ (Lafresnaye): Great Kiskadee.-- Apparently our specimens, which were in the late stages of breeding, are the first evidence of reproduction for the species on the peninsula. Specimens (4): [Female], 40663, ova to 1 mm., 50.7 gm. (July 9), and [Male], 40664, right testis 12 mm., 65.0 gm., body feathers in early stages of molt (July 9), 5 km. S Champotón; [Male], 40665, testis 5 mm., 61.9 gm., molting--middle pair of rectrices are new, 6th primaries ensheathed (July 15), 7-1/2 km. W Escárcega; sex? 40662, 59.5 gm. (August 14), 4 km. NNE Felipe Carrillo Puerto. Mallophaga: _Philopterus_ sp.