A NEW HYPSIGLENA FROM TIBURON ISLAND, SONORA, MEXICO Wilmer W. Tanner' Abstract.— Hypsiglena torquata tiburonensis is described as new to science from Isla del Tiburon, Sonora, Mexi-co. Notes pertaining to other taxa in the genus are inchided. The islands in the Gulf of California con-tinue to produce interesting variations in the genus Hypsiglena. Few islands are without representatives of the genus and all island populations show some variations not found in Baja California or Sonora populations. Those islands furthest from the coast and off the coastal shelf, such as Tortuga and Santa Catalina, show the most variation, an in-dication of their longer isolation. A most unusual pair of specimens is avail-able from the island of Tiburon. They are un-usual in their color pattern and particularly in the large number of dorsal spots. As noted above, it is not unexpected for island popu-lations to be differentiated from the mainland populations, but, considering the short dis-tance from costal Sonora to Tiburon, one would not expect such a radical departure in pattern. Because the population is distinct, I choose to name it— Hypsiglena torquata tiburonensis, n. subsp. Fig. 1 HoLOTYPE.-An adult female, BYU 33181, taken by James R. Dixon, on Isla del Tiburon, Sonora, Mexico, 14 August 1974. Paratype.-An adult female, MVZ 37802, taken by C. G. Sibley at Ensenada del Perro, Isla del Tiburon, 10 November 1941. Diagnosis.— A subspecies of Hypsiglena torquata characterized by light brown spots, which are narrowly separated from one an-other (usually less than one scale) and in-volving 7-9 dorsal scale rows. There is a strong tendency for the dorsal spots to be separated or only narrowly connected at the dorsal midline. In the holotype, the nape pat-tern is similar to deserticola, but in the para-type it is as in northern Sonora and Arizona specimens. The subspecies tiburonensis is most closely related to those nearby popu-lations in Sonora and Arizona and in the Great Basin, but it is distinct in the number, size, and shape of the dorsal spots. Description.— Rostral broad, rounded, and projecting anteriorly 0.7 mm, 17.5 per-cent of distance to anterior edge of frontal; loreals 1-1; preoculars 2-2; temporals 1-2; supralabials 8-8; infralabials 10-10, four rows of gulars between posterior chinshields and first ventral; ventrals 185; caudals 52; anal di-vided; dorsal scales in 21-21-15 longitudinal rows. Nape pattern of three dark blotches, the median one of these with three parts, the an-terior median portion narrow, extending from the parietal posteriorly 5 scales to fuse on each side with the lateral portions of this spot; lateral nape spots separated from me-dian and extending anteriorly to orbit; dorsal blotches on body 86, many divided or nar-rowly connected medially, spots separated by narrow pale cross-bands usually one-half scale wide, dorsal spots when united forming a band across dorsum involving 7-9 scale rows. Dorsum of head without dark spots; body color a light brown with narrow, cream-colored mottling separating the spots. Measurements.— Snout-vent length 376 mm; tail length 68 mm; tail 15.3 percent of total length; head length, from snout to pos-terior edge of parietals 11.4 mm; head width 10.5 mm; diameter of eye 2.1 mm. Remarks.— The size, shape, and number of dorsal body spots is the most distinctive char-acter in tiburonensis. There are other sub-'Life Science Museum, Brigham Young University, Provo, Utah 84602. 139
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