Specimens (19): [Male], 40565, brood patch, 59.4 gm. (July 9), [Male], 40564, testis 8 × 4 mm., brood patch, 68.0 gm. (July 9), [Male], 40566, 74 gm. (July 9), [Female], 40567, juv. (July 9), [Male], 40568, testis 5 × 3 mm., 68.3 gm. (July 10), [Male], 40578, 59.5 gm. (July 11), and [Female], 40577, ova to 2 mm., brood patch, 65.2 gm. (July 11), all from 5 km. S Champotón; [Male], 40560, 43.6 gm. (July 20), [Female], 40562, brood patch, 55 gm. (July 21), sex? 40561, 64 gm. (July 21), and [Female], 40563, juv. (July 22), Pisté. Eight nestlings (40569-76) that were taken from burrows at 5 km. S Champotón on July 11 had the following weights: 42.4 gm., 39.7 gm., 38.5 gm., 12.2 gm., 40.0 gm., 30.7 gm., 26.8 gm., 19.0 gm. Mallophaga: _Philopterus_ sp., July 9. _Momotus momota lessonii_ Lesson: Blue-crowned Motmot.--For convenience, the specimens from 5 km. S Champotón are assigned to _M. m. lessonii_ on the basis of measurements (wing 139 mm., tail 240 mm., culmen [from feathers] 41.0 mm.) taken on one specimen (40579), which are within the limits of the subspecies as described by Ridgway (1914). Two other specimens from that locality were prepared as skeletons and their weights are essentially the same as those Paynter (1955a) recorded for _M. m. lessonii_. According to Paynter, there is a southward clinal increase in size in this species between the smaller _M. m. exiguus_ in the northern part of the peninsula and _M. m. lessonii_ in the extreme southern part. A more extensive series of specimens from the vicinity of Champotón probably would reveal a population intermediate in size between the typical representatives of the two races. Specimens (3): [Female], 40579, 105 gm. (July 10), [Female], 40581, 98.9 gm. (July 11), [Male], 40580, 102.5 gm. (July 11), 5 km. S Champotón. _Pteroglossus torquatus erythrozonus_ Ridgway: Collared Aracari.--A male taken at Pueblo Nuevo X-can on July 27 and a female from 4 km. NNE Felipe Carrillo Puerto on August 15 had slightly enlarged gonads, which probably were regressing. Apparently these are the first indications of breeding activity for this species on the peninsula. Specimens (5): [Male], 40586, testis 4 × 2 mm., 155 gm. (July 16), 7-1/2 km. W Escárcega; [Male], 40582, testis 10 × 5 mm., 169.1 gm. (July 27), and [Female], 40583, ovary inactive, 137.3 gm. (July 29), Pueblo Nuevo X-can; [Female], 40584, ovary 10 × 6 mm., 169.5 gm. (August 15), and sex? 40585, 148.9 gm. (August 16), 4 km. NNE Felipe Carrillo Puerto. _Rhamphastos sulfuratus sulfuratus_ Lesson: Keel-billed Toucan.--This species was especially common west of Escárcega, where it was most often seen in small flocks of less than 10 birds. Presumably breeding had already occurred; four specimens had inactive gonads.