PLASTIC CHARACTERS. XXXI 



genera except Plerotes, in Dyacopterus (probably ; only one specimen 

 is known), and in Notopteris. The latter genus is the only Fruit-bat 

 that has lost both p' and p^.] 



Degeneration of chceh-teeth. — Probably owing- to adaptation to a 

 kind of food that requires little mastication, the cheek-teeth are 

 imusually narrow (sublii)ear)iii >S'^6'no>M/c<er?s (subgenus oiRovsettus), 

 a few species of Pigro/Jiw (particularly Pt. scapulatiis and ivoodfordi), 

 Plerotes { Epomophorus section), Sphcprias (Cjfnoptervs section), and 

 nearly all Macroglossina; (less so in Eoni/cteris and some species of 

 Syconycieris than in the other genera). The narrowing of the 

 teeth is not infrequently {Plerotes, many Maeroglossina;) accom- 

 panied by a degeneration of their surface structure (flattening of 

 crown). 



12. Anomalies in the dental formula. 



Notes have been taken, during the preparation of this Catalogue, 

 of any anomaly in the dental formula of the specimens examined. 

 Altogether forty-four cases have come under observation, i. e. 

 22 per cent, of the skulls examined exhibit individual aberrations 

 from the normal number of teeth. There can be no doubt, how- 

 ever, that for the large majority of Megachiroptera this estimate is 

 too liberal ; the fact is that of the forty-four cases no less than 

 twenty-three fall on forms distinguished by a more or less high 

 degree of degeneration of the cheek-teeth, a condition which appears 

 to be particularly favourable for the development of individual 

 dental anomalies (see the paragraph "■ Odontonycteris," p. 754; 

 the " genus " Odontonycteris was based on a Macroglossvs with a 

 supernumerary molar on each side above) ; it would probably be 

 approximately correct to saj^ that in any large series of skulls of 

 Macroglossus, Eonycteris spelcea, and Ptero]>7is scapvlottis at least 

 twelve per cent, will present anomalies in tlie dental formula, 

 whereas in all other Fruit-bats taken together the percentage has 

 been found to be only 0*9. 



The anomalies observed may conveniently be classed under the 

 following four headings : — (1) Absence of teeth which are normally 

 present in the species (it is hardly necessary to say that senile 

 conditions have been left entirely out of consideration, and that a 

 tooth has been considered " absent " only if there is no trace what- 

 ever that it has ever been present in the individual), this anomaly 

 in some cases " foreshadowing "' the permanent disappearance of the 

 same tooth in related forms : (2) Appearance of teeth which are 

 normally absent in the species, but present in related forms of 

 Itregachiroptera : (3) Appearance of teeth which are normally 

 absent in all Megachiroptera, but (since present in some Micro- 

 chiroptera) have probably been present in some ancestral form : 

 (4) Accidental outgrowths. Whether a case ought to be classed 

 under the fourth or third category is, as noted below, sometimes 

 doubtful. 



