NATURAL SCIENCES OF PHILADELPHIA. 385 



marked with black on each side near its base. Posteriorly the scales of the 

 first row are faintly marked with black at their bases. These black markings 

 are not prominent, and only perceptible upon close examination. The head, 

 including the upper labials and rostral, has more of an olivaceous cast. The 

 abdomen is entirely uniform pale greyish yellow, the tips of the scutella be- 

 ing, however, tinged with the ashy brown color of the back. 



1309, Durango, Mexico. Lieut. Couch. 



In its general aspect this species bears considerable resemblance to Nerodia 

 erythrog aster, from which, however, it is, upon critical examination, at 

 once distinguished by the number of dorsal rows and other generic characters. 

 It will, perhaps, be found that the faint black markings on the first, fourth and 

 eighth rows are the remaining indications of faded stripes. 



NERODIA Baird & Girard. 



N. Couchii Kennicott. 



Spec. char. Resembles N. erythrog aster, but the head is shorter 

 and very broad ; the muzzle broad and obtuse. Postorbitals three, much 

 larger than in N. erythrogaster, the lower extending forward beyond 

 the middle of the eye. Eight upper labials, all large, the seventh much 

 larger than in N. erythrogaster; the dorsal scales are broader and less 

 strongly keeled, and in twenty-three rows. Uniform dull light slaty brown 

 above, paler than erythrogaster. 



Descr. The head is short, but very broad and deep posteriorly ; the nose 

 is broad and obtuse. The outline presented by the head is subovoid, not 

 regularly tapering from the angle of the jaws to the snout as in N. erythro- 

 gaster. The prefontals are rather shorter than in that species. The post- 

 orbitals are very large, three in number, the lower one elongated forward to 

 beyond the middle of the orbit. The color above is entirely uniform dull 

 light slaty brown, lighter than in the lightest varieties of the erythrogas- 

 ter . The abdomen in both specimens examined is uniform brownish white. 

 Upon stretching the skin of one specimen, traces of the usual white transverse 

 lines are seen between the scales. The young are probably marked somewhat 

 as in N. erythrogaster. 



No. 1319, San Diego, New Leon. 143+1, 71, 23, 37|, 9|. Lieut. Couch. 



No. 1314, Santa Caterina, New Leon. 143+1, 86, 23, 26|, 9. Lieut. 

 Conch. 



This species very closely resembles N. erythrogaster, but can be 

 distinguished upon comparison by the lighter color, broader and shorter head, 

 and by the larger postorbitals and anterior position of the lowest. From N. 

 Woodhousei it differs in its uniform color, its much broader and shorter 

 head, etc. 



N. compressicauda Kennicott. 



Spec. char. Body stout. Form triangular, much compressed toward the 

 tail, where it is considerably higher than broad. Head elongated, rather 

 narrow, but very deep. Plates of the crown large ; vertical short, very broad ; 

 loral small; three postorbitals, upper and lower small, but the central with 

 its lower posterior angle prolonged to the labials. Twenty-one dorsal rows of 

 scales, all carinate, in form rather wide ; those of the first rows proportionally 

 small. Ground color yellowish olive ; four black stripes on the neck ; behind 

 this zigzag transverse black bands, which do not taper on the sides. Poste- 

 riorly these bands break into three series of spots symmetrically arranged, 

 not alternating. 



Descr. Body rather stouter than that of N. S i p e d o n , and presenting a 

 subtriangular form. This is most evident posteriorly, where, and on the tail, 

 the height is much greater than the transverse diameter. The tail is very 

 large at the base as in N. rhombifer, and does not taper from the anus, 



I860.] 



