 They have slender, firm bodies and narrow, slightly flattened heads with short to long, pointed snouts.The nostrils are divided into incurrent and excurrent openings by triangular flaps of skin on their anterior rims.The horizontally oval eyes are placed mostly on the sides of the head and equipped with rudimentary nictitating membranes (protective third eyelids); below each eye is a subtle ridge, and behind is a small spiracle (auxiliary respiratory opening).