258 BULLETIN 58, UNITED STATES NATIONAL MUSEUM. 



This key is not satisfactory for the determination of the last four 

 genera, and gi-eat care should be exercised in their identification. 

 Specimens referred to any of these should be tested by the other keys 

 and by comparison with the descriptions. There is no reliable external 

 character by which to distinguish our species belonging to Natrix from 

 those of Elaphe. However, a specimen with smooth or nearly 

 smooth scales (with pores) is usually an Elaphe, and when more 

 strongly keeled, if it has a small scale below the preocular (a sub- 

 preocular), it also belongs to the latter. Natrix never has this sub- 

 preocular. Zamenis has it, but can be recognized by the very long 

 and narrow shields on top of the head. 



The land snakes occurring in the four large islands of Japan can be 

 easily determined by the following artificial key: 



ARTIFICIAL KEY FOR THE IDENTIFICATION OF THE SNAKES OF JAPAN PROPER. 



a' A deep hole or pit between nostril and eye Agkistrodon blomhoffii, p. 457. 



a^ No hole between nostril and eye. 



¥ Subcaudals entire; no postoculars, temporals joining eye. 



Achalinus spinalis, p. 297. 

 b' Subcaudals in pairs; postoculars, separating temporals from eye. 

 c' Pupil vertically elliptic. 



d' Anal entire; a preocular Dinodon sem.icarinatum.,c- p. 366. 



(P Anal divided; no preocular Dinodon orientalc, p. 372. 



c^ Pupil round, 

 d' Scale rows 19. 



e^ Ventrals less than 170. 

 f^ Parietals equaling the distance from eye to tip of snout. 



Natrix tigrina, p. 272. 

 /- Parietals longer than distance from eye to tip of snout. 



Natrix vibakari, p. 266. 



e^ Ventrals more than 190 Elaphe quadrivirgata, p. 327. 



d? Scale rows more than 19. 



e^ Scale rows 21 Elaphe conspicillata, p. 334. 



e^ Scale rows 23-25 Elaphe climacophora, p. 324. 



The examination of the dentition must be made very carefully m 

 order to avoid mistakes. The safest way is probably to dissect out 

 one of the maxillary bones. This can be done very easily by running 

 the point of a sharp knife between the supralabials and the under- 

 lying bone, cutting the tissue along the whole length of the latter. By 

 forcing the point of the knife over the upper edge of the bone in the 

 region of the eye the bone can be easily lifted up and the connecting 

 ligaments severed. The adherent tissue may be carefully removed, 

 though in most cases it is sufficient to let it dry. The teeth can now 

 be examined conveniently. Care must be had not to mistake the 

 space left by a lost tooth for a natural interval; if a tooth has fallen 

 out, a distinct pit or depression is left on the alveolar edge of the max- 



« Occurrence in Japan very doubtful. 



