THE FAMILIES AND GENERA OF BATS. 
23 
lower incisors or Pterocyon are of the simple, little recurved type; 
the lower incisors of the former are straight, with bluntly rounded, 
slightly thickened crowns. Upper incisors of Pterocyon not seen. 
DENTAL FORMULA. 
The nearest approach in bats to the typical complete dentition of 
higher mammals — that is, a set of 44 teeth — as expressed by the 
formula 
12 3. 1. 123456 7,3-3 ^1-1 
12 3. 1. 123456 7* 3-3’ ° 1-V 
pm 
4-4 
m 3 - -3 =11. 
4-1’ '" 3-3 
is a set of 38, lacking one upper incisor and one upper and one lower 
, - 2 3. 1. - 2 3 4 5 6 7 
premolar: p 2 3 . 1 . _ 2 3 1 5 6 T 
38. The smallest number known is 
_ 2 _ 1 45 
20 , represented by the formula — * ^ = 20. Between 
these extremes occur no less than 50 formulas, representing totals of 
24, 26, 28, 30, 32, 34, and 36. No bat is yet known with 22 teeth. The 
following table shows the distribution of the various total numbers of 
teeth among the 173 genera now recognized : 
