THE FAMILIES AND GENERA OF BATS. 
31 
nearly straight, though usually marked by three projections and two 
indentations. The anterior border is unsymmetrically convex, the 
inner border variously truncate, rounded, or double convex, the 
posterior border with a concavity usually somewhat greater than con- 
vexity of anterior border. The inner posterior portion of the crown, 
bearing no large cusp, is usually flattened and often produced into a 
noticeable heel. The crown bears three main cusps, corresponding to 
those of the primitive tritubercular tooth, the inner anterior proto- 
cone (fig. 4, prc .), the outer anterior paracone (fig. 4, pc.), and the 
outer posterior metacone (fig. 4, me.). Not infrequently the inner 
posterior hypocone (fig. 4, he.) is also present, but in bats this cusp 
never attains a size sufficient to obscure the tritubercular aspect of the 
crown. Very rarely (in some Phyllostomidae, particularly Brachy- 
phylla , Plate VI, fig. 3) an intermediate cusp, the protoconule, occurs 
between protocone and paracone, and another, the metaconule, at 
inner base of metacone. At the extreme outer edge of the tooth are 
three small cusps, the anterior parastyle (fig. 4, ps.), the median 
mesostyle (fig. 4, ms.), and the posterior metastyle (fig. 4, mts.) a . 
The styles are connected wdth the main cusps of the outer row by four 
conspicuous, trenchant, slightly concave ridges, or flutings, the com- 
missures (fig. 4), the first extending from parastyle to paracone, 
the second from paracone to mesostyle, the third from mesostyle to 
metacone, the fourth from metacone to metastyle. The commissures 
are approximately equal in length, though increasing slightly from 
first to fourth. Together with the cusps, which they connect, these 
ridges form a conspicuous W-pattern, the variations in the form of 
which are of much systematic importance. Of the three main cusps 
the protocone is situated at a lower level than the others. In form it 
is more robust, though usually less elevated; frequently it occupies 
nearly the entire inner section of the tooth. A narrow commissure 
extends forward from anterior side of this cusp, past base of para- 
a In describing the molar teeth I have adopted the cusp nomenclature pro- 
posed by Osborn (See American Naturalist, XXII, p. 1072, December, 1888) 
as the most simple and convenient. The fact that it was based on a mistaken 
idea of the succession of cusps (See Gidley, Proc. Washington Acad. Sci., VIII, 
p. 106, July 10, 1906) is of little weight compared with the convenience of an 
exact name for each part of each tooth. The system of numbering the cusps 
(cusp No. 1—ps, No. 2 —ms, No. 3 =mts, No. 4— pc, No. 5— me, No. 6=pb, No. 
7 =hc, etc.) proposed by Winge (Vidensk. Meddel. Naturhist. Foren., Ki0ben- 
havn, 1882, pp. 15-19, pi. hi) and recently adopted by Andersen and Wroughton 
(Ann. Mag. Nat. Hist., 7th ser., XIX, p. 129, February, 1907) appears to be equally 
misleading as regards the succession of cusps, while it has the great disad- 
vantage of furnishing no convenient names. With regard to the position of the 
primitive cusp : Winge placed it in the outer row (mesostyle), Osborn in the 
inner row (protocone), while the observations of Gidley, based on much more 
extensive material, shows almost conclusively that it is in the middle row 
(paracone). 
