).2051. VARIATIONS OF THAMNOPHIS 0RDIN0IDE8— THOMPSON. 359 



POSITION OF THE VISCERA. 



The external landmarks of the principal viscera, in terms of gas- 

 trosteges, are as follows : 



In this table are recorded specimens in which the scale formula 

 is 19-21-19-17, the normal for this particular geographical region. 

 If compared with the two previous tables for the normal scale formula 

 several points of interest may be ehcited. The V row is usually 

 added, giving the maximum count of 21 rows, at the level of the base 

 of the heart, and becomes suppressed beyond the posterior half of the 

 liver where that organ begins to taper. The IV row is very con- 

 stantly suppressed, leaving 17 rows, just posterior to the gall bladder. 



There is no variation from the normal position of the viscera in 

 specimens with the abnormal or less frequently occurring scale 

 formulae. Where the count is 19-17, the IV row is usually suppressed, 

 exactly as in those with the normal formula, a little behind the gaU 

 bladder. 



- As to the length of the spinal column, it is clear that whatever 

 increase or decrease in the number of dorsal vertebrae that takes place 

 in an individual specimen is brought about by the addition or sub- 

 traction of vertebrae in that part of the column that is between the 

 posterior end of the left kidney and the base of the tail. 



HABITAT. 



The Sausahto Peninsula is bounded on the east by San Francisco 

 Bay and on the west by the Pacific Ocean; it is about 10 km. long 

 and 5 km. wide. The hills, many of which reach an altitude of from 

 200 to 300 meters, are almost bare of trees. The valleys are deeply 

 eroded and are clothed with fairly dense groves of laurel, scrub oaks, 

 manzanita, and willows. In all the canyons the brooks cease to flow 

 during the dry season, but in places water continues to trickle and 

 there are many damp spots and a few water holes. 



