THE FAMILIES AND GENEKA OP 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 1 2 3.1.128*567 .3-3 1-1 4-4 3-3 _ M 



t0rmula i23. 1.12345 67* 3^3' C T=V ^ m 4^4' m 3^3 ~ 44 ' 



is a set of 38, lacking one upper incisor and one upper and one lower 



- 2 3. 1. - 2 3 4 5 6 7 00 _, ., . , 



premolar: -ioq i _ q q 4, k a y = 38. lhe smallest number known is 



20, represented by the formula ~ ~" ' ~~~ , „ = 20. Between 



-2 3. 1. -2-45 — 



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 varipus total numbers of 



teeth among the 173 genera now recognized : 



