JOHN E. CADLE, CHARLES W. MYERS
American Museum Novitates 2003 (3409), 1-47, (22 May 2003) https://doi.org/10.1206/0003-0082(2003)409<0001:SOSRTD>2.0.CO;2
The name Dipsas variegata (Duméril, Bibron, and Duméril) has been applied to snakes disjunctively distributed in northeastern South America and in Panama and western South America. The specific name variegata is here restricted to populations occurring from Venezuela to Trinidad and French Guiana, and seemingly to the mouth of the Amazon in Brazil. Records from Colombia are unsubstantiated.
The name Dipsas nicholsi (Dunn) is revalidated for a Central American endemic with an exceptionally small range in central Panama. Specimens from western Ecuador previously assigned to “Dipsas variegata nicholsi” represent a different species—Dipsas andiana (Boulenger), which is resurrected from the synonymy of Dipsas oreas (Cope). Other records of Dipsas variegata from western Ecuador and southeastern Peru are based on misidentifications of species well known from those areas.
Dipsas nicholsi and D. andiana differ in some scutellation, hemipenial, and color pattern characters. The two species share an unusual head pattern, but data are insufficient to conclude that they are sister species, although their disjunct distribution pattern (Panama and Chocoan South America) is one shared by many other organisms thought to be phylogenetically related.
Hemipenes of Dipsas nicholsi and D. andiana are slightly bilobed and fully capitate; the sulcus spermaticus divides within the capitulum and has centrolineal branches. The capitulum is ornamented with papillate calyces. A battery of enlarged spines encircles the organ below the capitulum (with more spines in nicholsi than in andiana). There is an elongated basal nude pocket positioned laterally on the organ. Overall hemipenial morphology is similar to other species of the tribe Dipsadini (Dipsas, Sibon, Sibynomorphus, Tropidodipsas) for which organs have been described.
The Dipsadini are docile snakes that, in the authors' experience, never defend themselves by biting or even striking with mouth closed. Defensive positional deportment is nonetheless widespread and varied, most commonly including acquisition of a triangular head shape in at least three genera of Dipsadini (and other snakes as well), which is brought about by dorsolateral spreading of the quadratomandibular articulations. Either asymmetrical or symmetrical coiling and head-hiding also occur in diverse species; there is evident individual variability in some species, whereas others possibly lack specialized behavior. A specimen of Dipsas nicholsi did not show the common head triangulation, but repeatedly exhibited stereotypic stages of defensive positioning that resulted in it taking the shape of a raised spiral coil.