30 BULLETIN 43, UNITED STATES NATIONAL MUSEUM. 



LOWER MOLAKS. 



Antero-exterual cusp Protoconid. pr'' 



Postero-external cusp Hypocoiiid. liy'> 



Antero-interiial cusp or fifth cusp Paraconid. pa'^ 



Intermediate or autero-iuterual cusp (in quadritubercular molars) . . Metacoiiid. me"* 

 Postero-iuterual cusp Entocouid. en^ 



The upper molar in most bats presents to an extraordinary degree 

 depressions on the outer or buccal surface of the crown. Such depres- 

 sions receive the name of "tlutings" andareseeu in the teeth of many 

 mammals other than the bats, as for example in the moles and shrews 

 among the Insectivora, in the Ungulata, and in a marked degree in an 

 extinct genus described by E. I). Cope, Lamhdother'mm. "Flutings," 

 while of no homological significance, furnish systematic characters, and 

 will therefore be noted in the descriptions. Disposed so as to define 

 two V-i^^^n^ed figures the "flutings" extend as a sinuate commissure 

 between the paracone and the metacone. Of the two ys an anterior 

 and a posterior will be distinguished. Each V bas two limbs, a first and 

 a second. In the third molar various degrees of loss of the systciu 

 of flutings occur. Commonly the anterior V i^ retained while the se^-- 

 ond is lost, excepting the buccal half of the first limb, as in A. fuscus, or 

 the "fluting" is reduced to the anterior y, the palatal half of the sec- 

 ond limb being lost, as in Macrotus and Atulapha. In the bats of I^orth 

 America the least reduced last molars are seen in Nyctinomus and T^. 

 hesperus. 



The tritubercular tooth which results ii'om the presence of the three 

 cusps, the protocone, the paracone, and the metacone, may be con- 

 nected with a triangular figure by bands which unite the cns]>-points. 

 These bands will be named in this monograph the commissitres. In 

 the molars of the bat such a triangle is seen whose apex is palatal and 

 constituted of the lirotocone and whose commissure extends from tliis 

 cusp to the paracone and metacone. Its base is the extraordinarily 

 sinuate ("fluted") buccal surfiice of the crown. A careful search must 

 be made for the true positions of the sides of this triangular figure, for 

 they lie on the opposed sides of the teeth and are inconspicuous. The 

 crown at the " flutings" is of great vertical extent and dwarfs even the 

 proportions of the protocone. Wheu seen in profile the proportions 

 between the size of the "columns" of the two \/s and the "cusp" of 

 the protocone aftbrd materials for interesting comparisons in the differ- 

 ent genera. The hyi)ocone presents excellent subordinate characters. 

 It is a development of the cingulum. Usually flat, as in Macrotus, it 

 may be sharply defined as in Promops perotis or provided with a sharp 

 cusp as in the exotic genus NoctUio. The cingulum can be traced as a 

 delicate ridge which lies basal to the sides of the tritubercular triangle. 

 It varies greatly in extent, being best developed in N'yctinomus. 



In the lower molar scarcely any fluting is present and the plan of the 

 tooth is simple. The protoconid, paraconid, and metaconid are united 

 by commissures. The apex of the triangular figure is buccal. The 



