NATURAL SCIENCES OF PHILADELPHIA. 21 



tares of teeth presented by the most specialized divisions of the 

 hoofed mammalia, have been pointed out by the writer in an 

 essay On the Origin and Homologies of the Types of Dentition 

 of the Mammalia Educabilia. 1 From this discussion the analysis 

 of the most specialized sectorial tooth of the carnivora, as seen in 

 the Felidse, was omitted. As light has been thrown on the subject 

 by later researches, a note of the conclusions will be made here, 

 chiefly with reference to the dentition of the lower jaw. 



In the above essay I regarded the simple fonr-lobed or quadri- 

 tnbercnlate molar of the hypothetical Bunotherium as the starting 

 point of all more specialized forms of crested teeth. The second 

 and third lower molars of the peccaries (Dicotyles) represent such 

 a type. It was also pointed out that additional tubercles may be 

 added to this, or to a still simpler form, by the development of 

 basal cingula. 



The genus Hyopsodus presents a modified form of quadrituber- 

 culate molar ; in the genera Pantolestes and Antiacodon we observe 

 that the tubercles are similar, excepting that the anterior inner is 

 slightly bifid. In Pelycodus (whose systematic position is uncer- 

 tain) the two apices of this tubercle are separated more widely 

 from each other, so as to constitute two cusps. These are con- 

 nected with the anterior outer cusp by acute ridges which thus 

 form two sides of a triangular area ; the anterior ridge is evidently 

 a developed cingulum. 



The tubercular molar of some Viverridse, and among extinct 

 forms especially of the Didymictis protenus, Cope, presents a simi- 

 lar structure to that just described. This furnishes a ready expla- 

 nation of the tooth immediately in advance, which is the primitive 

 form of sectorial tooth characteristic of that t}-pe of carnivora. 

 The three anterior tubercles are largely developed, standing at 

 opposite angles of a triangular space; the outer and anterior 

 cusps are the most elevated, and the ridge which connects them is 

 now a short cutting blade. The posterior portion of the tooth 

 does not share in this elevation, and its two tubercles are in some 

 genera replaced by an elevation of one margin which leans obliquely 

 towards the middle of the crown. In Mesonyx this is rep'esented 

 by a median longitudinal crest. If the two tubercles of the pos- 

 terior part of this tooth (which may be termed a tubercular sec- 

 torial) are elevated and acute, we have the molar of many recent 

 and extinct Insectivora ; if the same portion, now called a heel, 

 is much reduced, we have the type of Oxysena and Stypolophus. 

 In the Canidse the three anterior tubercles are much less elevated 

 than in the genera above named ; the external is much the larger, 

 and the anterior removed further forwards so as to give the blade 

 a greater antero-posterior extent. The heel is larger and without 

 prominent tubercles. In the Mustelidse the inner of the two 

 median cusps is often reduced to a rudiment, or is entirely wanting, 



1 Journal of the Academy of Natural Sciences of Philadelphia, 1874. 



