42 BULLETIN 57, UNITED STATES NATIONAL MUSEUM. 



an extra cusp behind the protoconid, while the upper canine has a 

 new cusp on the outer side of its tip. In Niadius the extra canine 

 cusp is at the posterior base, while the additions to the cheek teeth 

 take the form of small terete cusps near middle of crushing surface. 

 The latter region is occupied by a longitudinal ridge in Dolsonia. 

 In Pteralopex and Harpyionycteris the tendency toward supernu- 

 merary cusps is carried to the greatest extreme, the penultimate cheek 

 tooth of the latter, both above and below, containing no less than 

 three well-developed, subequal cusps on each side, the resulting form 

 closely resembling that of the molars of the Jurassic Bolodon. 



The last series of changes leads to the cutting teeth of the sanguiv- 

 orous bats. The chain of intermediate stages is here less complete 

 than in that leading to the fruit-crushing type, as the teeth of the 

 Desmodontidae are so excessively modified a? to stand quite alone. The 

 first step in this direction may apparently be seen, however, in the 

 Hemiderminse and in the genus Erophylla. 



The teeth of Hemiderma (Plates IX and X, fig. 1) are not con- 

 spicuously different from those of Glossophaga. The mesostyles have, 

 however, completely disappeared, and the parastyles and metastyles 

 have practically lost their identity in the large bases of the paracones 

 and metacones. The two outer main cusps are well developed, and 

 their edges, together with what remains of the commissures, are 

 strongly trenchant. Protocone low, short, and rounded, widely sepa- 

 rated from the outer cusps and forming entire inner section of crown. 

 In the lower molars the original cusps may all be traced, but those of 

 the outer row stand not far from middle of crown, where they form 

 a nearly straight cutting edge, while those of the inner row are much 

 reduced. The paraconid is present, however, in all three teeth, 

 though in the first it is less developed than in the others, while the 

 entoconid, though low and indistinct, is present as a postero-internal 

 rim in all but the last. The process of reduction begun in this genus 

 is carried much further in Rhinophylla. The protocone has here prac- 

 tically disappeared, being represented by a mere inner rim to the 

 outer cusps, which now stand close to lingual side of crown. The 

 paracone and metacone are low and very narrow, producing a faintly 

 two-lobed cutting edge ; paracone lower than metacone. On the outer 

 side the crown is relatively wide, and the basal remnants of the 

 parastyle and metastyle are evident. The corresponding changes in 

 the lower molars have resulted in a form of crown scarcely dis- 

 tinguishable fiom that of the premolars, except by their slightly 

 greater length and more distinct main cusp (protoconid). On close 

 inspection the last trace of the hypoconid may be detected, appear- 

 ing in profile as a mere backward prolongation of the median cutting 

 edge, but showing a distinctly indicated thickened base when viewed 

 from above. 



