Hypsirhina matannensis Boulenger, 1897: 225. Holotype: NMB 1735. Type locality: Lake Matana, Celebes (Sulawesi, Indonesia).
Enhydris matannensis: Haas, 1950: 576.
Hypsicopus matannensis Murphy and Voris 2014:26.
Diagnosis: This snake has 21 scale rows at mid-body, a single postocular scale, and a divided internasal that does not contact the loreal scale. Enhydris enhydris may be sympatric with this species and also has 21 scale rows at mid-body, but it has a single internasal that does contact the loreal. E. enhydris has a striped dorsal pattern this species is uniform in color. Hypsicophis plumbea is its sister species and it has 19 scale rows at mid-body, the internasal is usually single, and it has two postocular scales.
Etymology. The name matannensis refers to Lake Matana, the type locality for this species.
Distribution. This species is endemic to Sulawesi, and is known from the type locality, Lake Matana, (~02°27’S 121°12’E), Sulawesi and near Raha (~04°51’S 122°43’E), on Muna Island in the southeast Celebes (Sulawesi).
Size. Iskandar (1979) reported a female as having a total length of 563 mm and a 78 mm tail. The type specimen, also a female has a total length of 452 mm with a 65 mm tail. Thus the tail/SVL ratios for females of this species are 16 and 16.7%.
External Morphology. The head is slightly depressed, the body is cylindrical, and the tail is mostly round. The eyes are dorsolateral and the eye-nostril distance is about 1.25 times the diameter of the orbit. On the head the rostral is pentagonal and visible from above, and about twice as broad as tall. The nasals are in contact, and are large (wider than the frontal). They are completely divided with the nasal cleft touching the first labial and the internasal. The nostrils are directed dorsally. The internasal is divided and is not in contact with the loreal in the type specimens. The prefrontal scales are about twice the size of the internasal scales and are in contact with the loreal. The frontal is about 1.5 times as long as broad and is pentagonal. The posterior margin is divided. The parietals are slightly longer than the frontal. The loreal is quadrangular and about as long as tall; and in contact with upper labials 2 - 3. The single supraocular has a narrow anterior margin and a broader posterior margin; preocular is taller than broad; postocular is taller than broad; no subocular scales, the fourth and fifth upper labial enter the orbit. The temporal formula is 1 + 2 + 3. The ventral secondary temporal is larger than the one above it. There are eight upper labials, the seventh is the largest.
On the chin the lower labials number 10, the sixth is the largest, and the first five contact the anterior pair of chin shields. Gular scales number four. There are two pairs of chin shields, with the first pair longer than the second. The chin and head scales are tuberculate.
On the body the dorsal scales are in 21 rows on the neck and at midbody, and they are reduced to 19 rows in front of the vent. The scales are smooth, and the first three rows are large with the scales get smaller toward the midline of the dorsum. They have no ornamentation in the specimen examined. Ventral scales number 139. They are about 2.5 - 3 times the width of a nearby dorsal scale. The anal plate is divided. The ventral preceding it is wider than the other ventrals. There are two tuberculate scales lateral to the anal plate on both sides.
On the tail the dorsal scales on the tail are similar to those on the back. The subcaudal scales are divided and number 43. The tail of the female type specimen is 16% of the SVL. At the base of the tail the width is 86% of the height in one specimen.
Color and Pattern. The head is a uniform brown with the head plates having a light outer margin. The upper labials have a light lower margin. All of the dorsal scales are a uniform brown with the exception of the first row. These have slightly lighter lower margin. There are light spots on the lower labials 5 - 7. The anterior chin shields are mottled. The ventral scales are cream and each has a dark central spot which is narrow anterior and widens posteriorly. The ventral surface of the tail has a midline stripe.
Habitat. A female, collected from a fish pond, about 100 m from the coast and about 200 m from the nearest river was reported by Iskandar (1979). This snake is known from a relatively few specimens and its diet and reproductive habits remain unknown.