56 HETERODON. 



broad. Keel acutely distinct. Scales on the back of head keeled, 

 though obsoletely in those next to the occipital plates. The line from 

 tip of snout to lower angle of posterior labial, crosses the lower part 

 of the eye, whose centre is a little in advance of the middle of this 

 line. Orbital chain of 9 plates. Loral triangular, truncated above. 

 Nasals rather large, less developed than in H. platyrhinos. Upper 

 labials 8 ; 3d-6th in contact with suborbitals. Centre of eye above 

 the juncture of the 4th and 5th. 



Scales distinctly carinated, except the outer row, which is smooth, 

 and the second, on which the carination is very obsolete, sometimes 

 quite smooth. All the scales diminish gradually to the back, where 

 they are quite linear ; posteriorly, however, they are broader. 



Color above and on the sides entirely dull black, beneath rather 

 light slate-color, shading into milk-white on the chin and on the edge 

 of the upper labials. The exterior rows of scales shade gently from 

 the color of the back to that of the belly. 



The Heterodon niger bears quite a close relationship in the cha- 

 racter of the plates and scales to 11. jjlafp-hinos, from which the 

 principal difference lies in the color. Although this species greatly 

 resembles in color the black variety of JI. atmodes, they may be 

 readily distinguished. The rostral of S. niger is well developed, 

 high, broad, and with the dorsal carina acute and well marked. The 

 carination on the scales back of the head is delicately distinct, as also 

 upon the other scales, the keel extending to the very tip. The scales 

 on the back are linear and narrow, but become much broader in pro- 

 portion towards the tail. The occipitals are longer, and the head in 

 front of the eye longer in proportion to the part behind it. No bands 

 evident, even obsoletely. The other differs in all these respects : 

 rostral low, and the keel more rounded; scales on back shorter, 

 and anteriorly rather broad, and the disproportion with those posteri- 

 orly much less conspicuous; carina) not extending to the tip; faint 

 bars seen indistinctly across the black of the back, &c. 

 Carlisle, Pa. 9 140+1.49.25. 36.6. S. F. Baird. 



Specimens from the South differ simply in being rather darker on 

 the sides and beneath. 



Ahheville, S. C. 145+1. — 25. 26. — Dr. J. B. Barratt. 



Kemper Co., Miss. 126+1.53.25. 28. 5|. D.C.Lloyd. 



