Common names: Sri Lankan hump-nosed viper.

Hypnale nepa is a venomous

Venomous snake

"Poisonous snake" redirects here. For true poisonous snakes, see Rhabdophis.Venomous snakes are snakes which have venom glands and specialized teeth for the injection of venom...

 pitviper

Crotalinae

The Crotalinae, commonly known as "pit vipers" or crotaline snakes, are a subfamily of venomous vipers found in Asia and the Americas. They are distinguished by the presence of a heat-sensing pit organ located between the eye and the nostril on either side of the head...

 species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 found in Sri Lanka

Sri Lanka

Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...

. Relatively small, they are distinguished by a strongly upturned snout. No subspecies

Subspecies

Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

 are currently recognized.

Description

Adults grow to a total length of 30–35 cm. According to Wall (1921), the maximum recorded lengths are for a male of 38.7 cm and a female of 38.1 cm. According to Deraniyagala (1955), the largest specimen in the Colombo museum was 39.2 cm in total length with a tail measuring 5.9 cm. In general, the tail is 13-18% of total body length. The body is moderately slender with a head that is conspicuously distinct from the neck.

This species is distinguished from H. hypnale

Hypnale hypnale

Hypnale hypnale is a venomous pitviper species found in India and Sri Lanka. No subspecies are currently recognized.-Description: Grows to an average of 30-45 cm in length. The Armed Forces Pest Management Board states 0.4-0.6 m in length....

 by a snout that has a strongly upturned tip. This is due to an extended rostral scale, which is immediately followed by a raised wartlike hump covered with 7-14 very small scales. Also, the hemipenes

Hemipenis

A hemipenis is one of a pair of intromittent organs of male squamates .Hemipenes are usually held inverted, within the body, and are everted for reproduction via erectile tissue, much like that in the human penis. Only one is used at a time, and some evidence indicates males alternate use between...

 have clearly visible spines.

The scalation includes 17 rows of dorsal scales

Dorsal scales

In snakes, the dorsal scales are the longitudinal series of plates that encircle the body, but do not include the ventral scales.When counting dorsal scales, numbers are often given for three points along the body, for example 19:21:17...

 at midbody that are weakly keeled

Keeled scales

Keeled scales refer to reptile scales that, rather than being smooth, have a ridge down the center that may or may not extend to the tip of the scale, making them rough to the touch...

 or smooth, 124-142 ventral scales

Ventral scales

In snakes, the ventral scales are the enlarged and transversely elongated scales that extend down the underside of the body from the neck to the anal scale. When counting them, the first is the anteriormost ventral scale that contacts the paraventral row of dorsal scales on either side...

 and 33-41 subcaudal scales

Subcaudal scales

In snakes, the subcaudal scales are the enlarged plates on the underside of the tail. These scales may be either single or divided and are preceded by the anal scale....

.

The color pattern consists of a light brown to dark brown to pale olive ground color, flecked and mottled with darker tones. This is overlaid with a series of 17-26 dorsolateral suboval or subtriangular brown blotches that alternate or oppose each other middorsally. These blotches are 3-4 scales wide and extend down to the third scale row. The top of the head is brown and usually lacks any pattern except for a black postorbital stripe that extends to the neck.

Geographic range

Found in Sri Lanka

Sri Lanka

Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...

 throughout forested areas, from lowland rainforest to over 1,800 m altitude. The type locality given is "Africa." An obvious error, this was amended to "Sri Lanka" by Hoge and Romano-Hoge (1981).