HOMALOCRANIUM. 147 
narrow, straight, white, transverse collar, crossing the neck behind the occipitals. No 
white spots on the head. Lower parts white. 
Two specimens, 7 inches long, of which the tail takes nearly 2. 
8. Homalocranium melanocephalum. 
Coluber melanocephalus, Linn. Mus. Ad. Frid. p. 24, t. 15. fig. 2; Syst. Nat. i. p. 378 [the species 
described by Daudin under this name is a compound of different forms ; and that by Kuhl 
(Beytr. p. 87) belongs to an Indian genus]; Boie, Isis, xx. p. 526 (1827). 
Natriz melanocephalus, Merr. Tent. p. 110. 
Elaps melanocephalus, Wagl. in Spix, Serp. Brasil. p. 8, t. 26. fig. 1. 
Cloelia melanocephala, Wag]. Syst. Amph. p. 187. 
Calamaria melanocephala, Schleg. Ess. ii. p. 38, t. 1. fig. 30. 
Homalocranion melanocephalum, Dum. & Bibr. Erpét. vii. p. 859; Jan, Iconogr. Ophid. xy. t. 2. 
figg. 4,5; Bocourt, Miss. Sc. Mex., Rept. p. 588, t. 37. figg. 4, 4 a—d. 
Tantilla melanocephala, Cope, Proc. Ac. N. Sc. Phil. 1871, p. 205; Journ. Ac. N. Sc. Phil. viii. 
p. 144 (1876). 
Cloelia dorsata, Wagl. Syst. Amph. p. 187. 
Tantilla armillata, Cope, Journ. Ac. N. Se. Phil. viii. p. 143 (1876). 
Hab. TropicAL AMERICA. 
Head flat, depressed; eye about half as long as the snout. Vertical shield rather 
elongate, longer than broad. Seven upper labials, one ante- and two postoculars ; 
temporals 14-1. ‘The first pair of lower labials form a suture together. Scales in 
fifteen rows, without apical groove. Ventrals 137-162; anal divided: subcaudals 
44-62. Upper parts brownish, with a black dorsal line, which sometimes is very 
indistinct, and may be entirely absent ; sometimes with a dark line along each side. 
Head and neck black above, with symmetrical whitish markings, which, however, are 
by no means constant; sometimes the snout is white, and a pair of occipital spots are 
present, which may expand into a collar; the black coloration of the neck is usually 
margined with white behind. A white spot behind the eye is nearly always present. 
Lower parts whitish. 
The synonymy and description given above embrace individuals collected from a 
wide geographical range, and more or less slightly varying from each other. Schlegel, 
Duméril and Bibron, myself, and Jan included the whole under one specific name—- 
melanocephalum; and in a general work in which the whole of the variations have to 
come under consideration it is, perhaps, more convenient to treat of them in the form 
of varieties of one specific type, while in the account of a more restricted fauna a 
strictly binominal method may be adopted, if the variations can be duly characterized. 
I propose, therefore, to arrange first the materials before me of Homalocranwum melano- 
cephalum (in the wider sense) in a synoptical table, and afterwards separately to 
describe the Central-American forms :— 
*19 2 
