Cope.] 226 [Dee. 21, 
animal is mature but not old, as the second true (third intermediate) molar 
is present and much worn, and the last molar is worn on its anterior three- 
fifths. 
The posterior or fourth crest of the second true molar is narrower than 
the third, and is not followed by a heel. The third molar presents six 
transverse crests, and so large a heel that it might be said to be seven- 
crested. Each crest is sub-transverse, and is composed of a principal ob- 
tuse cone at each extremity and some smaller ones between, in close con- 
tact. The apices of the larger ones approach each other, and the median 
ones are less elevated. The section produced by wearing of the third and 
second crest each, is that of two trefoils placed base to base, and the lateral 
lobes of these, completely close the valley between those crests. The val- 
leys between the other crests are closed by one or two distinct median 
tubercles, and the sections of those crests are less accurately trifoliate than 
those of the others. There is a very large cingulum at the anterior ex- 
tremity of this tooth whose worn section is confluent with both of the 
trefoils of the anterior crest near the middle. A portion of it is isolated on 
the inner side of the crown, forming a flattened cone, or when worn, an 
isolated oval with the long axis directed inwards and forwards. This I 
have counted as the first crest, as it is as much entitled to it as the one so 
counted by Dr. Falconer, in the 7. stvalensis. The palate is narrow, not 
exceeding the width of the second true molar. 
The mandibular rami are of rather light tissue, and are compressed in 
form, the external face being little convex. The symphysis is produced, 
without abrupt contraction either laterally or below, into a robust beak 
whose depth is equal to the width five inches beyond the bifurcation. It 
is channeled above by a narrow and deep groove, and supports no tusks. 
From the appearance of the tissue when fractured transversely it is evi- 
dent that there have been no alveolar cavities at any time. The beak is 
slightly decurved and the extremity is depressed and transversely flat- 
tened. The superior incisor possesses a broad band of enamel, which 
covers nearly one-third the diameter of the tooth. 
Measurements. M. 
Length of crown of second true molar................. 118 
Width ae ae MGS Nb dsaiatilss's panne eres 075 
Length we third f Conwegiesda se oaaacs 195 
Width os ae BES. osu Macsdrnce ta ae aote -080 
sf palate at anterior extremities of second molars .045 
e sia posterior crests of third me 095 
Length of ramus from posterior border to bifurcation.... .560 
Length of symphyseal beak (broken).................. -480 
Depth of do. five inches from bifurcation........... see «118 
WidthOf dO.8t dOwwsiccd aecnkesven ¢oinas jokoenenys 115 
This fine new Mastodon is the second species of the genus Tetralophodon 
found as yet in North America, the first being the 7. mirificus of Leidy. 
