On the Classification of the Cavies. 303 
M* more complicated, with heel long 
and separated from the rest of the 
posterior lobe by a deep notch ...... 2. Caviella, Osg. 
Genotype, C. australis, Geoff. & D’Orb. Other species: C. menas, 
hos, 
r 
6°, Incisors much thrown forward, their 
angle with the line of the tooth-row 
about 115°. J* less complicated, the 
heel a mere short triangular projection, 
without internal notch ............ 3. Monticavia, g. n. 
Genotype, M. niata (Cavia niata, Thos.). Other form: M. niata 
palidior, Thos, 
6. Skull not specially shortened. Incisors 
pigmented, directed backwards, their 
angle about 85° with the line of the 
tooth-row. Orbital branch of maxillary 
completely interrupted by lacrymal.... 4. Galea, Meyen. 
Genotype, G. musteloides, Meyen. Other species: G. boliviensis, 
Waterh., auceps, Thos., syia7, Wagl., flavidens, Brandt, wellsi, Osg., pa- 
lustris, Thos. 
6. Toes with nails. Skeletal characters de- 
Sembed: py Ospood.(2e!)e:5 kets skid sos 5. Kerodon, F. Cuv. 
Genotype, K. rupestris (Cavia rupestris, Wied). 
this way a more exact measurement might be obtained. But this involves 
the anomaly that teeth which appear to the eye approximately vertical have 
a measured index of about 75°, instead of 90°, while teeth with a measured 
angle of 90° are in reality what one calls “ thrown forward.” The object 
of all such measurements being to give a more exact method of expres- 
sion to eye-judgments, I would propose now to alter the measurement, to 
make it more in conformity with the general impression. 
This may be done by adjusting one limb of the goniometer to the 
chord of the curve shown in side-view by the whole exposed part of the 
tooth, from the highest external corner where it issues from the bone to 
the tip of the tooth. The other limb is then adjusted parallel with the 
tooth-row, this being easily done by eye, and the resulting angle read off. 
As explained before, specimens with properly developed incisors, neither 
pulled out nor pushed in, are necessary, and it is also essential that the 
examples should be without imperfections in the bone at the point 
where the incisors leave it. 
The resultant angles are all, of course, considerably higher than before, 
and I now give the angles in the same animals measured in the revised 
way. Rattus listert comes out at 52° instead of 26°-28°, R. rattus 70° 
80°, R. berdmorei about 100°. Rhizomys 82°-87°, Nyctocleptes 97° or 98°, 
Bathyergus about 105°, Cannomys 112°-115°; while in the most extreme 
form of all, Heliophobius, the angle is about 180°. A Canadian beaver 
stands at 90°, a Cynomys at 95°, and an Ondatra at 96°. 
As before, a fairly large limit of error must be allowed; but this does 
not seem to be greater in the new way, which undoubtedly gives a truer 
idea of the angle at which the incisors are set. 
Instead of a goniometer, a simple protractor may be used, and the 
angle judged by eye; but in that case the limits of error would un- 
doubtedly be larger. Even then, however, there is a gain in exactness 
as compared with the old vague statements of “ incisors thrown forward” 
or “ directed backward,” without any effort at measurement at all. 
