Hypsirhina
(Eurostus) jagorii Peters, 1863 Monatsberichte der Preussischen Akademie der Wissenschaften zu Berlin, p. 245. Type
locality: "Siam." Restricted here to the vicinity of Bangkok,
Thailand. Holotype: ZMA 4746.
Hypsirhina
smithii Boulenger, 1914 Journal of the
Natural History Society of Siam 1:69. Type locality: Mivam Chao Phraya,
Bangkok, Thailand. Holotype: - BMNH 1948.1.7.27.
Enhydris
smithi – Smith, 1929 Journal of the
Natural History Society of Siam 8:50.
Enhydris
innominata smithi - Saint Girons 1971 Société
du Science Naturelles Physiques du Maroc, 51:221.
Comment
This species has been confused with
two other species in museum collections since Günther (1864). Examination of
the type specimen revealed that it was not conspecific with either of the two
species labeled Enhydris jagorii in
museum collections. One of those species is Enhydris
chanardi, the other is Enhydris
subtaeniata (see that account for an explanation). A redescription of the
holotype is provided here, and the rational for placing Hypsirhina smithii Boulenger in the synonymy of E. jagorii is also provided. For a
comment on its relationship to E.
longicauda and E. innominata see
the E. innominata account.
Etymology: This
snake was named in honor of Dr. F. Jagor, who made a collection of reptiles in
Thailand for the Zoology Museum in Berlin.
Distribution Enhydris
jagorii is known only from the vicinity of Bangkok, Thailand, although Smith
(1915) obtained a specimen from Hua Hin Beach (12°34’0N 99°58”0E) about 200 km
south of Bangkok in Prachuap Khiri Khan Province. It is also known from the
Bang Kapi area (presumably Bang Kapi District) just to the east of Bangkok
(based on an unnumbered NSM specimen) and an area now considered part of the
Bangkok metropolitan area. The type specimen of Boulenger’s (1914) smithii is from the “Menam River” (=Chao
Phrya River) in Bangkok. Another specimen (FMNH 179114) has the data Phra
Nakhon (presumably Phra Nakhon District), Bangkok; thus, this aberrant patterned
specimen is most likely from the city center of Bangkok. It is unclear if the
Hua Hin specimen represents a population, or a waif, washed down the river into
the Gulf of Siam. Note that Tirant (1885) refers a specimen from Cholon,
Vietnam (~12°15’N 105°58’0E) to Enhydris
jagorii because it had 106 ventral scales; clearly this is a specimen of E. innominata given the locality and
ventral count which is too low for Enhydris
jagorii. Reports of Enhydris jagorii
from Laos, Vietnam, Cambodia, and elsewhere in Thailand are based on specimens
of Hipsirhina enhydris subtaeniata Bourret.
Diagnosis: A snake with 21 scale rows at midbody
that can be distinguished from other Enhydris
with 21 scale rows by the flared or petal-shaped anterior chin shields which
are longer than the posterior pair of chin shields. Ventral scales number 117 -
127, this will usually separate it from its closest relative E. innominata which has 108 - 117
ventral scales with which it shares a pattern of scalloped black blotches that
arise from ventral side and extend onto the dorsum. Its close relative E. chanardi has 21 scale rows on the
neck (jagorii has 23 to 25 on the
neck) and two pairs of chin shields with the second pair as long as or longer
than the anterior pair. E. chanardi lacks
the black scalloped pattern and has a wide, bold zigzag stripe on the edge of
the ventral scales and first scale row, clusters of scales with dark pigment
that form lateral spots, and a ventral count of 110 - 125 (this overlaps with jagorii). E. jagorii’s black scalloped blotched pattern will separate it from
E. enhydris which has a longitudinal
striped pattern and it has elongated chin shields with the second pair being
longer than the first, and a ventral count greater than 153. E. subtaeniata also has 21 scale rows,
but elongated chin shields (two or three pairs), a striped pattern on scale
rows 1 - 3, dark lateral spots on the scale rows above the stripe, and a
ventral count of 136 - 153. E. jagorii
can be most readily separated from its close relatives E. longicauda and E.
innominata by their ventral counts (jagorii
has 117 - 127 ventral scales, longicauda
has 124 - 135, innominta has 108 - 117).
Size: The largest specimen measured (BMNH 1928.12.18)
was a female with a snout-vent length of 445 mm and a damaged tail. The next
largest female had a total length of 515 mm with a 93 mm tail. The largest male
had a total length of 471 mm, with a 118 mm tail. The smallest specimen
measured (NSM 0925) was a female with a total length of 238 mm and a 43 mm
tail. Nine specimens examined had SVLs ranging from 195 - 445 mm (= 327 mm). Three males had tails that were 29 - 33%
of the SVL; five females had tails that were 22 - 26% of the SVL.
External Morphology
The head is moderately long, wider
than neck, and appears intermediate in width between innominata (narrow head) and longicauda
(wide head). The head is not as depressed as in either of the other two snakes.
Eyes are dorsal and their diameter is about 80% of the eye-nostril distance.
The eyes of this species are quite large compared to those of innominata
and longicauda.
On the head the rostral scale is
pentagonal and twice as broad as tall. The nasal scales
are semi-divided, with the nasal cleft touching the first labial. The broad internasal can be single or divided and it contacts loreal
scales. The prefrontals touch the loreal, preocular, and
supraocular. The frontal is slightly longer than the parietals. The
supraoculars are rectangular; the posterior edge is wider than the anterior
edge. The loreal is in contact with upper labials 1 - 3.
It is usually single but one specimen (BMNH 1928.12.18.1) has a divided loreal.
The preocular is single and tall, its dorsal edge is narrower than the ventral
edge; there are two postocular scales, and the upper scale is taller than the
bottom scale. The temporal formula is 1 + 2; the primary temporal is taller
than broad, but even it is very similar in size to the occipital scales and is
barely distinguishable from them. The upper labials number eight (87.5%) or
nine (12.5%). The tallest upper labial is the sixth or seventh, the fourth
upper labial enters the orbit and it too is large; rarely the fifth upper
labial enter the orbit.
On the chin the lower labials number
10 or 11; the largest is six or seven. Labials 1 - 4 or 1 - 5 contact the
anterior chin shields. Anterior chin shields are longer than the posterior pair
and they are flared or petal-shaped . A small pair of
scales separates the posterior chin shields from each other. Gular scales
number 9 - 10.
On the body the anterior scale rows
on the neck number 23 - 25. Scale rows at midbody number 21. Scale rows at posterior
body are reduced to 19 - 20. There are no scale ornaments, and the scales become
more ovate posteriorly particularly in the more ventral rows . Scales in the first row are larger than those in the second row. The tail
is slightly compressed, to about the same degree as in innominata. Ventral scales number 117 - 122 in three females
examined; males have 117 - 127. The ventrals are rounded; and wide, about three
times the height of a nearby dorsal scale. The anal plate is divided, and
slightly longer than a ventral.
On the tail the subcaudal scales are
divided and number 48 - 54 in females and 53 - 68 in males; thus, subcaudal
counts are sexually dimorphic. Dorsal scales are smooth and ovate and counted
from the base of the tail they form 12 - 13 rows. At the base of the tail the
width is 83% of the height based upon one specimen.
Color and Pattern. The head is
uniform; labials may have some yellow spots or mottling. Vertebral spots number
about 38 and occur on scale rows 10 - 14. Spots on scale rows 1 - 8 and 1 - 9
form a series of large lateral blotches that are 2 - 3 scale rows wide.
Sometimes the vertebral row fuses with the spots on rows 8 - 9 to form small
bars. There are about 38 large dark blotches each 2 - 3 scale rows wide. The
lateral blotches are separated by yellow or white bars less than one scale
wide. These white or yellow cross bars intrude onto the venter so that they
completely encircle the body, forming a pattern of yellow or white rings.
Natural
History
Like other homalopsaids they eat small fish, and give live birth. or reproduction of this species. Its distribution suggests it is endemic to the
Chao Phraya freshwater swamp forest ecoregion of the Indochina Bioregion
(Wikramanayake et al., 2002). It seems likely that this snake’s habitat may
have been greatly reduced in the last century with the urban sprawl of Bangkok
consuming much of its known distribution; thus this species may be endangered.
In 2006 we rediscovered a population of these snakes in northern Thailand. The masthead for this website depicts one of the specimens we collected.
Relationships
This species is closely allied to E. chanardi, with which it is sympatric
and to the allopatric E. innominata
and E. longicauda. It represents the
most northern species of the group, and remains a poorly known taxon despite
its distribution in the heart of Bangkok.