1. MWELODERMA. 301 
1. HELODERMA. 
Trachyderma (non Latr.), Wiegm. Isis, 1829, p. 421. 
Heloderma, Wiegm. 1. c. p. 624; Wagl. Syst. Amph. p. 164; Wiegm, 
Herp. Mex. p. 23; Dum. § Bibr. iii. p. 499; Gray, Cat. p. 14; 
Bocourt, Miss, Sc, Mev., Rept. p. 296. 
ANATOMICAL AND PuysroLocicaL: Troschel, Arch. f. Nat. 1853, 
p. 294, pls. xill, & xiv.; Swmichrast, Arch. Sc. Phys.-math. xix. 1864, 
p. 45; AKaup, Arch. f. Nat. 1865, p. 33, pl. iii.; Cope, Proc. Ac. Philad. 
1869, p. 5; Gervais, Journ. Zool. 1873, p. 458, pl. xii.; Sumichrast, C. R. 
Ac. Se. Ixxx. 1875, p. 676; Bocourt, l. c. p. 299, pl. 206; Sumichr. Bull. 
Soc. Zool. France, 1880, p. 178; Fischer, Verh. Ver. Hamb. v. 1882, p. 2, 
pl. ili.; Shufeldt, Amer. Nat. 1882, p. 907; Bouleng. Proc. Zool. Soe.. 
1882, p. 631; Fayrer, eod. loc. p. 632; Mitchell § Reichert, Med. News, 
1883, and Science, i. 1883, p. 372. 
Ear exposed. A gular fold. Digits with a series of transverse 
lamelle inferiorly. Upper surfaces uniformly tubercular; abdo- 
minal scales flat, juxtaposed. Labial shields present. 
Mexico. 
1. Heloderma horridum. 
Heloderma horridum, Gray, Cat. p. 14. 
Hernandez, Hist. Nov. Hisp. p. 315. 
Trachyderma horridum, Wiegm. Isis, 1829, p. 421. 
Heloderma horridum, Wiegm. Isis, 1829, p. 624, and Herp. Mex. 
p. 24, pl.i.; Daum. & Bibr. p. 499, pl. xxxvi.; Bocourt, Miss. Se. 
Mex. p. 297, pl. xx. B. figs. 1-12; Giinth. Biol. C-Am., Rept. 
pl. xxvi. 
Head depressed; snout short, broadly rounded; lips thick. 
arcuate, the lower much swollen ; nostril large; eye small, with 
very thick lids; ear-opening elliptical, vertical, slightly oblique ; 
chin-groove strong; gular fold well marked. Body elongate, rather 
depressed. Limbs moderate; claws strong, of the fingers much 
longer than of the toes. Tail cylindrical, tapering, about as long as 
the body. Upper surface of head covered with large, convex, irre- 
gular, bony tubercles; rostral broad, pentagonal ; nostril between 
four plates, the largest inferiorly ; a pair of large internasals between 
the two pairs of anterior nasals; ten or eleven upper and about 
twelve lower labials; mental small, subtrapezoid ; chin with large 
polygonal plates; throat with | round or oval convex tubercles. 
Body and limbs covered above with subequal round convex tubercles 
separated by a granulate skin: about thirty-five tubercles across the 
middle of the body. Abdominal scales flat, subquadrangular, longer 
than broad, in about fifty-five series between the gular fold and the 
preanal region, and about twenty across the middle of the belly. 
Caudal scales subequal, tubercular above, flat and subquadrangular 
inferiorly, arranged in rings. Blackish brown above, spotted with 
yellow, the latter colour sometimes forming regular rings round the 
tail. 
