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B. c.
occidentalis Natural History Articles
We
wish to thank C. R. Smith for kindly providing this description.
Journal
for the Unified Natural Sciences Herr Dr. Segeth has had brought to him at various times boa constrictors found on the other side of the Cordillera in Mendoza and San Juan Provinces, yet most died during transport over the Cordillera and only one arrived alive at Santiago where, meanwhile, it also lasted only a few weeks and died for no reason to my knowledge. Our museum has acquired in this way two skins and the freshly dead snake that Herr Landbeck has stuffed. We have initially considered it the common Boa constrictor with which it agrees completely as far as the top of the head is concerned, but the coloration, however, is very different and the snake may so merit a type of its own to be set up that one can name it Boa occidentalis. Herpetologists who have numerous examples of Boa constrictor of the different Brazilian forms at their disposal may decide whether one should consider the snake from Mendoza as a mere Brazilian variety. The stuffed example measures 7 feet 10 inches from the tip of the snout to the end of the tail of which length the tail occupies only 72 inches. The head length amounts to 22 inches from the tip of the snout to the corner of the mouth and only 32 inches to the beginning of the neck; its width amounts to 2a inches. The greatest thickness of the animal at midbody is 3 inches. - I count 32 scale rows from the median line of the back to the belly shields; the number of belly shields amounts to 251, and that of the caudal plates to 45. The nose is covered with approximately 30 plates; approximately 20 circle the eye, 21 are on each side of the upper lip, and 15 shields stand in a diagonal line between the eyes. The rostral plate is somewhat taller in the Boa from Mendoza than in B. constrictor, but otherwise of the same shape; the chin plates differ only insofar as their margins are straight and not curved concavely. The foremost shield of the eye margin is in the same condition as in the Brazilian form. The coloration is conspicuously different and much darker overall in that the light ground color takes up less room than the brown markings, which also differ in condition from that in Boa constrictor, and on the belly each shield itself is darkly spotted. The top of the head is also divided by a long brown stripe, the rear brighter and cleft through the midline. Right and left of the snout is also a darker spot that reaches nearly to the anterior edge of the eye; behind the eye it reaches through a curved whitish line to the opening of the mouth, separated from the scarcely brighter cheeks. These are brightened by two whitish diverging lines arising from the edge of the eye and bordered by another whitish line that goes from the eye to the corner of the mouth. The temporal and parietal areas are dark brown and are separated by a lighter brown stripe from the dark midline of the head, just as itself is brightened by another lighter longitudinal band in the middle. The region between the nose and eyes shows darker nearly tesselated spots. - The back, which exhibits about 15 dark rectangular blotches in Boa constrictor, has 28 of them in the Boa from Mendoza, and these are notched before and behind and supplied with a lighter spot in the middle. The intervening area between these blotches forms more or less regular, longitudinally elongate hexagons that are bordered outside with a whitish margin that gives way gradually to a brown color on the inside. Each of the darker dorsal blotches is bordered on the sides by a whitish longitudinal line. While Boa constrictor itself shows eight to ten brick red tail blotches enclosed with dark ebony pigment, its tail is plain dark brown above, brighter and whitish below, and without markings on the sides. The sides of the body do not show a row of large brown blotches with whitish centers on a lighter ground as with Boa constrictor, but a wavy continuous band on a brown ground, sharply bordered above and below by a brighter yellowish margin and a gradually duskier light brown after the midbody; under each recessed angle of this band is a light blotch that sets off the brown color of the sides from the lighter belly with a sharply defined, continuous wavy line. These differences in pattern appear to me to be significant, though I could consider the questionable snake a mere color variety of the ordinary Boa constrictor, only -as said- it is impossible to compare it to a large series of pictures or whole examples of the latter, so I must forgo a decisive opinion. According to the men who brought it to Santiago and to other people from there, the Mendoza snake is not particularly rare in Cuyo, a province of Argentina that belonged formerly to Chile, and is called Lampatagua there. It stays especially in the holes made by the viscacha, Lagostomus trichodactylus, which animal is supposed to comprise its primary food; but it will sometimes stay in houses where it is entirely inoffensive and preys on rats and mice. It is supposed to be slower than other snakes in its movements. It is not supposed to be found, however, in the immediate vicinity of the city of Mendoza. My figure depicts the top of the head in its
natural size and a portion of the midbody in side view at half size. [Translated by C.R. Smith, Austin, TX 78745. March 2, 1992] The Original Occidentalis Description In German
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