78 Zoological Society. 



On a New Snake from the Galapagos Islands. 

 By Dr. Albert Gunther. 



The genus Herpetodryas, being composed of those Dryadidce 

 which have the maxillary teeth of equal length and entirely smooth, 

 comprises snakes from America and from Madagascar. The follow- 

 ing species comes from the Galapagos Islands, and appears to be the 

 only Snake as yet known to inhabit that group •. 



Herpetodryas biserialis. 



Diagnosis. — Scales in nineteen rows ; eight upper labials, three 

 posterior oculars. Light brown, with a dark-brown dorsal band, 

 serrated on the anterior portion of the trunk, and formed by a double 

 series of spots on the middle and on the posterior part of the back. 

 A dark-brown streak from the eye across the cheek. Belly irregu- 

 larly dotted with brown. 



Hab. In Charles Island (Galapagos). Typical specimen in the 

 Collection of the British Museum. 



Description. — The head is rather depressed, flat, and, like the 

 trunk and tail, somewhat elongate ; the eye is of moderate size, with 

 the pupil round. The rostral does not reach to the upper surface 

 of the snout ; the anterior frontals are square, the posterior ones 

 about twice the size and subquadrangular ; the vertical is rather 

 slender, twice as long as broad ; the occipitals triangular and rather 

 pointed posteriorly. The nostril is situated between two shields ; 

 the loreal nearly square ; the anterior ocular extends to the upper 

 surface of the head, and is in contact with the vertical. There are 

 three posterior oculars, the middle of which is the smallest, the in- 

 ferior forming a part of the lower portion of the orbit ; the temporal 

 shields are scale-like and rather irregularly arranged. There are 

 eight upper labials, the fourth and fifth coming into the orbit. The 

 median lower labial is triangular, and of moderate size ; ten lower 

 labials, the first of which is in contact with its fellow, behind the 

 median shield. There are two pairs of elongate skin-shields of equal 

 size. The scales are perfectly smooth, in nineteen rows, rhombic, 

 those of the outer series being rather larger. Ventral plates 209 ; 

 anal bifid; caudals 108. 



The ground-colour is a light brownish-grey : a vertebral band, 

 formed by dark brown spots, begins from the occiput, and is gra- 

 dually lost on the middle of the tail ; it is continuous anteriorly, and 

 serrated on both sides, but gradually dissolved into two series of 

 brown spots, the spots of each series being confluent on the end of 



* The first mention of a Snake on these islands seems to be in Dampier's ' Voy. 

 Round the World,' ed. 7. vol. i. 8vo. Lond. 1729, p. 103 : — " There are some Green 

 Snakes on these islands ; but no other land-animal that I did ever see." 



Darwin says in his Journ. of Research., p. 381, speaking on the Zoology of 

 the Galapagos Islands s — " There is one snake which is numerous ; it is identical. 

 as I am informed by M. Bibron, with the Psammophis Temminckii from Chile." 

 Although subsequently, in the ' Erpetologie Generate,' nothing is mentioned by 

 Dumeril and Bibron about the occurrence of P. Temminckii, or of any other snake, 

 in these islands, that determination of Bibron may possibly be correct. If such 

 be the case, there are two species of Snakes in that group of islands. 



