8 



BULLETIN 17 5, UNITED STATES NATIONAL MUSEUM 



the forms may serve to illustrate the organs for the entire genus (fig. 

 6). The hemipenes are slightly bilobed, with the sulcus spermaticus 

 simple and running diagonally across the organ to the tip of one of the 

 lobe?. The anterior two-thirds of the surface is smooth, except for 

 several shallow irregular longitudinal furrows and a large number of 

 minute spinules scattered irregularly over the posterior two-thirds of 

 this area. On the opposite side from the sulcus there is a noticeable 

 elongated ovoid prominence. The posterior third of the surface is 

 covered with irregular rows of calyces, each calyx bearing a terminal 

 spine. On either side of the sulcus in this region there is a narrow 



Figure 3.— Head of Pituophis sayi affinis: a, From the side; 6, from above. 



smooth border. In the accompanying drawing of the hemipenis of 

 sayi sayi (fig. 6), the organ has been dissected open, and the muscle 

 removed from the posterior end. 



The dentition is as follows: Mandibular teeth 16 to 22, decreasing 

 slightly in size posteriorly; maxillary teeth 14 to 18, sohd and without 

 a diastema, decreasing slightly in size posteriorly; palatines 7 to 12, 

 slightly smaller than the mandibular and maxillary teeth, but rela- 

 tively stouter; pterygoids 6 to 14, smaller than the palatines and de- 

 creasing in size posteriorly. 



The fundamental type of pattern throughout the genus is spotting. 

 Most forms bear a median dorsal series of large dark, more or less 

 quadrangular spots on a light ground. In most cases thereMs one or 

 more additional alternating series of spots on either side. In lineati- 



