AMERICAN BATS — HANDLEY 103 



size and apparently is the first to disappear. It is most reasonable 

 to assume that these same factors may have operated to eliminate the 

 missing incisor. The first to go then, at a very early stage of 

 chiropteran development, was probably I^ This is in agreement with 

 Andersen's (1908, p. 205) and Thomas' (1908, p. 348) criticisms of 

 Miller's conclusions. 



Premolars: Since the number of premolars in each maxiEa and 

 mandible in all known bats is at least one less than the primitive 

 placental number, it is assumed that one has been lost from each jaw. 

 Thomas (1908, p. 347) argued convincingly that the missing tooth is 

 the second. Miller (1907, p. 28), without proof, arbitrarily assumed 

 it to be the first. Evidence at hand possibly supports Miller's thesis. 

 A specimen of Plecotus townsendii (USNM 81647) has four premolars 

 in one mandible; the other ramus is normal. The extra tooth is on 

 the lingual side of the tooth row, adjacent to the normal anterior 

 premolar and forcing that tooth to the labial side of the row. Both 

 teeth touch the canine. The extra tooth is smaller than the normal 

 anterior premolar and rather like P3 in size and shape. If it were to 

 be assumed that this extra tooth reflects a primitive condition in 

 which the normal mandible bore four premolars, then it would be 

 necessary, because of its position, to assume that the extra tooth is Pi. 

 However, the argument refuting similar evidence for the missing 

 incisor can be applied with equal propriety here. 



Besides lacking, as do all bats, P2 in maxilla and mandible, Euderma 

 and Plecotus also lack another maxillary premolar. In this instance 

 the missing tooth is probably P^. An examination of Myotis in this 

 connection proves instructive. This genus normally lacks only a 

 single premolar, assumed to be the second, in each jaw. In some forms 

 the remainmg premolars normally are not even crowded (e.g., M. 

 lucifugus). However, other forms (e.g., M. occultus) frequently lack 

 two premolars in each jaw. The tooth that is variable in occurrence 

 is the third premolar. In 15 specimens of M. occultus P^ was present 

 in 4, absent in 11 ; P3 was present in 14, absent in 1. P^ normally is 

 absent in Plecotus, but occasionally is present (USNM 265387, 

 297711). In these specimens P^ is present in only one maxilla, is 

 similar to P' but is smaller, and is wedged between P^ and P* (postero- 

 internal to P^, on the lingual border of the tooth row). The "extra" 

 tooth in each instance is similar in form and position to P^ of Myotis 

 occultus. These teeth perhaps represent the normal third premolar 

 and not merely abnormal accessory teeth. They thus may be 

 authentic reversions to a primitive condition. 



In addition, the third mandibular premolar normally is lacking in 

 Euderma. In Plecotus it is present, but is smaller than either Px or P4. 

 In the subgenus Corynorhinus it is commonly squeezed between the 



