Hypnale walli, or Wall's hump-nosed viper,[2] is a venomous pitviper species endemic to Sri Lanka. The smallest member of its genus, it is distinguished by having a strongly upturned nose and lower scale counts. No subspecies are currently recognized.[3]
The specific name, walli, is in honor of Ceylonese-born British herpetologist Frank Wall.[4]
The smallest member of the genus Hypnale, the only male with a complete tail measured 30.5 cm (12.0 in) in total length with a tail of 4.3 cm (1+3⁄4 in) (14% of total length), while the largest female was 28.3 cm (11+1⁄4 in) in total length with a tail of 3.5 cm (1+1⁄2 in) (12% of total length). The body is stoutly built.[2]
This species is distinguished from H. hypnale by a snout that has a strongly upturned tip. This is due to an extended rostral scale, which is immediately followed by a raised wart-like hump covered with 10 minute scales. Also, the hemipenes have clearly visible spines. It is distinguished from H. nepa by its lower scale counts.[2]
The scalation includes 17 rows of dorsal scales at midbody that usually lack keels, 7 supralabial scales, 120-126 ventral scales, and 28-33 subcaudal scales.[2]
Regarding the color pattern, Gloyd and Conant (1990) examined a number of preserved specimens, mentioning that some were so faded as to render the pattern almost invisible. One of these, however, had a faint narrow stripe down the center of its back. In general, the color pattern is described as consisting of a series of 18-24 dorsolateral small subtriangular brown blotches, pointing upwards. These are slightly darker than the ground color, except for the upper edges that may be considerably darker. A pair of dark brown blotches are present on the side of the head, along with a pair of dark stripes curving backward on the sides of the neck. The ventral surface is strongly flecked and dappled with grayish brown.[2]
Hypnale walli is found in Sri Lanka. The type locality given is "Kanneliya Forest, Udugama Southern Province, Ceylon [Sri Lanka], elevation approximately 1,000 ft [300 m]".[1]
According to Gloyd and Conant (1990), the taxonomic status of this species is unclear. Although described here as a species, it may eventually be classified as a subspecies of H. nepa, or even as the minimum extreme for H. nepa with regard to its low ventral and subcaudal scale counts, as well as its relatively short tail.[2]
Hypnale walli, or Wall's hump-nosed viper, is a venomous pitviper species endemic to Sri Lanka. The smallest member of its genus, it is distinguished by having a strongly upturned nose and lower scale counts. No subspecies are currently recognized.
