ANATOMY OF THE OPHIDIA. 415 



result of this the crowded puhnonary tissue seeks the direction 

 of least resistance, which is along the tracheal membrane. 



In recording the position of the viscera it has been found 

 advantageous to adopt the following routine with the view of 

 correlating the data obtained. The serial number of the gastro- 

 stege that underlies the anterior tip or the posterior extremity 

 of an organ is taken as the external landmark. This number is 

 reduced to a percentage, the total number of the ventral shields 

 in the specimen being used as the base. From this procedure 

 there results a set of figures which will materially aid in com- 

 paring one species with another or in learning the extent of the 

 variation which the individuals of a given form exhibit. 



It appears that wlienever a serpent varies widely in an 

 important character from one of the natural groups, a further 

 investigation regularly results in the finding of several additional 

 structural features that are well worth making a matter of 

 record. The single species constituting the family of Xenopeltidte 

 may be taken as an illustration of this general statement. 



Some Notes upon Anatoviy. 

 Xenopeltis unicolor Reinhardt. (Text-figs. 77 & 78.) 



Specimen. No. 16750, California Acad. Sci. Singapore. 

 Female ; total length 480, tail 58 mm. 



Squamation. — Scales in 15 rows anteriorly, and the same 

 posteriorly, an oblique series commencing at one gastrostege 



Text-fio-. 77. 



A B ^ 



Teeth of Xenopeltis unicolor. 



A. Maxillary bone viewed at a right angle to the outer edge, and showing the 



oblique fashion in which each tooth is set in the jaw. 



B. Profile view of the same teeth, showing the lateral cutting-edges of the cusp. 



C. Palatine tooth viewed from below, and showing a stout and blunt tip which 



exhibits a tendency to assume the arrow-head shape of the cusps. 



terminates at the ninth ventral shield to the rear. Gastrosteges 

 177. Anal divided. Urosteges 32 pairs, the second entire. Loreal 

 and prseocular absent. Postoculars 2. Anterior temporals 2, 

 posterior 3. Supralabials 8, the fom-th and fifth entering the 

 eye. Infralabials 9. 



