188 PROCEEDINGS OF THE ACADEMY OP [1819. 



Gliddon, and now in the Museum of the Academy, present all the 

 normal details of structure of Cants 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. f ; C. \\ P. m. ; M. f ; inferior sectorial 

 without internal tubercle. The incisive formula might with pro- 

 priety read , since these teeth are shed at an early age ; and for 

 the same reason the tuberculars might be stated {, 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, I admit that 

 the possibility of its having come off from Canis rather than from 

 Synagodus is worth} 7 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. ; C. } ; Pm. J; M. h. 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 I 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 cateo;orv. 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 contraiy, in 



