1958 Homalopsis buccata - Taylor
and Elbel, University of Kansas Science
Bulletin 38:1159-1162.
1970 Homalopsis buccata
nigroventralis Deuve, Serpents du
Laos, p.183-185, Plate 21, Figures 1-4; Plate 22 Figs 1-3, 7. Type
locality: Nam Ngum River Valley, Laos. Type specimen: None designated, and
Deuve’s specimens may have been destroyed.
2006 Homalopsis nigroventralis
Stuart et al. Raffles Bulletin of Zoology
54:149.
Etymology
The name nigroventralis is from the Latin niger for black and venter for belly.
Diagnosis
This species is
readily separated from H. buccata by
the dark ventral surface with light lateral spots, 35 - 39 scale rows at
midbody, 10 - 13 upper labials, 14 - 17 lower labials, and 3 - 4 postoculars.
Populations of H. buccata in the
Mekong region have: white venters with a row of dark spots laterally, they have
40 - 45 rows of dorsal scales at midbody, 12 - 14 upper labials, 17 - 19 lower
labials, and 2 postoculars. Additionally, the frontal scale on the H. nigroventralis tends to have the
posterior edge fragmented, while H.
buccata does not.
Distribution
Homalopsis
nigroventralis is known from the Nam Ngum river valley of Laos, the Phu
Phan Mountain region (Sakon Nakhon district and province) of Thailand, and in
Cambodia in the Ta Veng and Sien Pang areas. The Thailand specimens were
collected at about 550 m (Taylor and Elbel, 1958), the Cambodia specimens were
collected between 100-170 m (Stuart et al., 2005).
Size
The largest specimen
measured was a 1032 mm male with a 204 mm tail, the largest female was 991 mm,
with a 171 mm tail that was damaged. The smallest specimen had a total length
of 287 mm with a 72 mm tail. Males have tails that are 33 - 35% of the SVL;
females have tails that are 27 - 32% of the SVL.
External Morphology
Like H. buccata, the head is slightly depressed,
distinct from the neck; the area behind the angle of the jaw is puffed out
giving the head a swollen appearance. The upper jaw extends over the lower jaw.
The body is cylindrical and the tail is partially compressed at the base and
becomes more compressed distally. The eyes are medium sized, and they are
positioned more lateral than most other homalopsids.
On the head the
rostral scale is pentagonal and narrow, usually taller than broad. The nasal scales
are semi-divided, in contact, large, and dorsal and the nasal groove contacts
the first labial. The internasal is divided, and isolated from the loreal. The
frontal scale is pentagonal, and is fragmented into several smaller scales at
the posterior edge. The parietals are paired and shorter than the frontal in
length. The loreal is usually single and contacted by upper labials 1 - 3 or 1 -
4. The ocular ring is composed of a supraocular; preoculars may number one (Thailand
population) or two (Cambodia population); and postoculars can number two
(Thailand population) or 3 or 4 (Cambodian population) in number. Suboculars
are present and number 1 - 4, the Cambodia population tends to have one or two,
while the Thailand population tends to have three or four. Temporal scales are
scale like and the temporal formula is often 3 + 3 or 3 + 4, but the Cambodian
population contains some individuals that have 1 + 3 or 2 + 4. Upper labials number
10 - 13, with 11 (44% of 18 sides) and 12 (44% of 18 sides) being the most
frequent. The first divided upper labial is usually number six and the first
few form two tiers of scales; the more posterior ones show three tiers of
scales. Upper labials five and/or six are usually under the orbit. On the chin the lower
labials number 14 - 17, with 16 (44% of 18 sides) and 17 (33% of 18 sides)
being the most frequent. Lower labials 1 - 3 contact the first chin shield.
Chin shields may number three or four pairs that are elongated. The first
divided lower labial is usually number 8 - 9. Gular scales number 10 - 13. On the body the dorsal
scales are strongly keeled and striated, with the usual exception of the first
row that usually lacks keels and has weak striations. On the neck the rows can
number from 36 - 38, at midbody the counts vary from 35 - 39, and in front of
the vent the number of rows varies from 26 - 28. Ventral scale are broad counts
range from 155 - 167, with three females having 155 - 160, and six males having
159 - 167. On the tail the
subcaudal counts for snakes with complete tails are 67 and 78 in two females
and 78 - 87 in four males.
Color and Pattern. In
preservative, these snakes take on a dark red-brown coloration with the typical
banded pattern seen in
H. buccata.
However, they have an irregular cream line that runs from the angle of the
mouth posteriorly along the third and fourth scale rows, this becomes broken
into spots. Additionally there is a cream line from the nasal scale, below the
eye, to the angle of the mouth. The occipital region has a pair of large cream
spots. The ventral pattern is black-brown with lateral cream spots and some anterior
transverse bars (Plate 35, Figures E and F). Bryan Stuart (personal
communication) described the color in life as follows. A juvenile male (FMNH
263033) had light orange dorsal body bands, a broad tan band on the dorsal
surface of head, a broken cream-white ventrolateral stripe connecting the dorsal
body bands, a distinctive white X-like marking on the chin, and a black venter
with scattered white spots. Three adults (FMNH 263030-32) had a brown dorsum
with faint, lighter banding that disappeared posteriorly and an olive brown
head with black markings on the snout and over eyes. The color of the venter
was yellow-olive (FMNH 263030, male), olive (FMNH 263031, female), or
olive-brown (FMNH 263032, male), darkening posteriorly to dark gray, becoming
very dark gray under the tail, with cream-white spots on the ventral scales and
subcaudal scales, beginning on the throat as a single spot on each ventral
forming a longitudinal line, becoming more scattered posteriorly but sometimes
arranged in pairs. The X-like marking on the chin was creamy-white.
Natural History
Stuart et al. (2005)
reported this snake from gravel bottom and bedrock streams (3 - 8 m wide) transecting
bamboo and mixed evergreen forest. Two specimens were collected during the day;
two others were taken from a gill net. In Deuve’s (1970) original description
he noted that this species and H. buccata
never occurred together.