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 Dobsonia. 
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 
Desmodontidse are so excessively modified as 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 Hemiderm ,a (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 Rhino pliylla. 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 f i om 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. 
