21 
Gliddon, and now in the Museum of the Academy, present all the 
normal details of structure of Canis familiaris. / 
The reduction in the number of teeth has been carried further, 
and is probably of more modern origin in the new genus to be 
described below. 
Dysodus, gen. nov. 
The characters of this genus, already indicated in the analytical 
table, are as follows: I. 3; C.4; P. m.2; M. 2; inferior sectorial 
without internal tubercle. The incisive formula might with pro- 
priety read 9, since these teeth are shed at an early age; and for 
the same reason the tuberculars might be stated 1, since the last 
one of the upper jaw is equally evanescent. I, however, give the 
genus the benefit of the possible future discovery of species in 
which the teeth in question may not be so early caducous, and 
rely on the restricted diagnosis. It is thus apparent that the 
genus Dysodus is distinguished from Synagodus by the absence 
of two premolars from each jaw. While the genera agree in other 
respects, their typical species are very different. 
This genus probably diverged from that now represented by 
Synagodus, at a comparatively late period. Although it exhibits 
a degree of dental reduction greater than that form, 1 admit that 
the possibility of its having come off from Canis rather than from 
Synagodus is worthy of consideration. This is suggested by the 
fact that the remaining (first) tubercular molar of the inferior 
series is, in D. pravus, more like that of the species of Canis in 
all respects, among others, in having two roots. 
In D.'pravus the superior third premolar is sometimes shed, 
like the incisors, having the formula, I. 2; C.4; Pm.34; M.3. I 
have excluded this character from the generic diagnosis, as in the 
case of the incisor and superior tubercular teeth, because they are at 
the present time unstable; that is, the parts in question are in pro- 
cess of metamorphosis. When characters are thus variable, they 
cannot be used as the bases of natural divisions, but when they 
are stable, we are compelled to recognize them. ‘The characters 
which J have included in the diagnoses of Synagodus and Dysodus 
I have thought to be of this character, and I am by no means sure 
that the absence of the superior incisor teeth should not be placed 
in the same category. But none of these characters, whether 
stable or unstable, can be regarded as monstrosities, such as mul. 
tiplied digits, fissured palate, etc. They are, on the contrary, in 
Q* 
