The South American genus Atractus barely enters political North America on the eastern half of the Isthmus of Panama, where it is extraordinarily rare. Collected over a period of 39 years, the five Panamanian specimens of Atractus known to the author represent five species! Four new species are described: A. darienensis, A. hostilitractus, A. imperfectus, and A. depressiocellus. The fifth species is A. clarki Dunn and Bailey, for which a second specimen is reported from the Colombia Chocó. The noncapitate hemipenis of A. clarki may be primitive in being calyculate and deeply bilobed.
The morphologically convergent Geophis is primarily a Middle American genus—Mexico to western Panama, with two or three outlying species in the western Andes of Colombia (G. betaniensis, G. nigroalbus, and probably G. hoffmanni). The genus is unrecorded from eastern Panama, and a few old records for central Panama seem to have been based on erroneous specimen data. Nonetheless, the genus does occur in east-central Panama, based on two specimens of G. hoffmanni (W. Peters) and on a specimen each of Geophis bellus, new species, and G. brachycephalus (Cope)—the latter representing a disjunct population separated by about 340 km from those in the Boquete area of western Panama.
Geophis bellus is a tiny snake differing from sympatric G. brachycephalus and South American G. nigroalbus in characters of size, color, and hemipenis. Geophis brachycephalus may be a composite species in western Panama. Unicolored specimens from the Atlantic versant seem to differ from those in the polymorphic Boquete population in hemipenial and other characters, and they are set aside as a species inquirenda. The first specimen of Geophis hoffmanni is reported from Colombia, but it lacks precise data.
Atractus depressiocellus, A. imperfectus, Geophis bellus, G. brachycephalus, and G. hoffmanni are at least broadly sympatric on the “Piedras-Pacora Ridge”—the continental divide—between the upper drainages of the Río Chagres and Río Pacora, some 30 km northeast of Panama City. This relatively low upland likely is a premontane forest refuge, where some very rare snakes may be making a last stand prior to extinction.
