MEXICAN TAILLESS AMPHIBIANS 31 



some small temporary pool. Under normal conditions, if mated in 

 the water, the female begins laying at once, and according to species 

 may lay from 600 to 16,000 eggs, the process usually being completed 

 within one day unless there should be a sudden drop in the tempera- 

 ture. The eggs are generally laid in long spiral strings of jelly, which 

 are attached to or which come in contact with some submerged object. 

 One species, B. pundatus, does not deposit the eggs in strings, but 

 singly or in a scattered mass. The inner tube of the egg string is 

 absent in B. compactilis but present in B. valliceps. The length of 

 the hatching period depends upon the temperature. Below 65° F. it 

 requires 8 to 12 days, and above that temperature 3 to 8 days. Warm 

 weather speeds up the rate of development and shortens the total 

 time in the egg and tadpole stages. Toads are thus born in the water 

 and in it spend their early life in a larval, fishlike state, breatliing by 

 means of gills. The transformation of the tadpole to a young toad 

 takes place some time between 30 and 65 days after hatching, and 

 imder abnormal conditions 200 days have been required. 



KET TO MEXICAN SPECIES OF BUFO 



1. Elongated gland extending full length of ulna; oval gland on 



upper surface of thigh and an interrupted gland on superior 

 surface of tibia; parotoid gland long, oval, and nearly as 

 large as side of head, descending on shoulder; tympanum 

 large, two-thirds the diameter of orbit; supraciliary cranial 

 crest forming regular curve with more elevated postorbital 

 crest; a narrow preorbital crest; one or more prominent 

 warts posterior to rictus oris; first finger longer than second; 

 smooth leathery skin, with scattered warts; grayish or 

 brownish green above; underparts light; size large, head-and- 



body length, 125 to 160 mm alvarius (p. 35) 



No elongated glands on ulna and tibia 2 



2. Parotoid gland subtrlangular in outline and nearly as large as or 



larger than side of the head 3 



Parotoid gland smaller than side of the head 4 



3. Parotoid glands divergent, very large, each extending backward 



to a point beyond shoulders, and covered with small tubercles; 

 a small indistinctly margined tympanum almost contiguous to 

 orbit; short-legged, small-bodied, with rough granular or 

 tubercular skin on upperparts and top of head; supraciliary 

 and postorbital crests indistinct; greenish or bluish slate 

 above, with small blackish spots; eyelids with oblique cross- 

 bar; tarsal fold with row of warts; metatarsal tubercles 



insignificant; head-and-body length, 40 to 75 mm debilis (p. 50) 



Parotoid glands divergent, unusually large, and studded with 

 large pores; a distinctly margined tympanum, about one-half 

 width of eye; skin of upperparts warty, interorbital region 

 generally smooth; prominent cranial crests, including 

 canthal, preorbital, supraciliary, parietal, postorbital, orbito- 

 tympanic, and supratympanic; interorbital space wider than 

 upper eyelid; coloration of upperparts variable, ranging 



