TRICONODON, OW.
Sp. Triconodon mordaz.—This name is proposed for a small zoophagous Mammal, whose generic distinction is shown by the shape of the crowns of the molar teeth of the lower jaw, which consist of three nearly equal cones on the same longi tudinal row, the middle one being very little larger than the front and hind cone ; and these cones are not complicated by any cingulum or accessory basal cusp.
The convex condyle is below the level of the alveoli, and there is no angular process projecting beneath it. The co ronoid process is broad and high, with its hinder point not extended so far back as the condyle ; the depression marking the insertion of the temporal muscle extends nearly to the lower border of the jaw. There are the obscure remains of three broken incisors, and the point of apparently a canine ; next come the two stumps, or broken roots of a small premolar ; then the crown of a second double rooted premolar, which show a principal cone and a small anterior cusp ; the next tooth is wanting ; then there is a larger premolar, with the two fangs raised some way out of their socket : the crown of this tooth shows a principal cone, with a small anterior and large poste rior talon ; it rises, apparently from partial displacement, higher than the succeeding molars ; these are three in number, and present the characteristic three-coned structure already described ; each cone is smooth, and convex externally. The
three cones seem to answer to the three middle or principal cones of the molars of Amphilestea and Phascolotheriurn, but the front and hind cones are raised to near equality with the middle cone in Triconodon.
The lower jaw of this species, in the relation of the condyle to the lower border, resembles that of Phascolotheritinn more than that of Antphitherium, but it differs from both ; there is not the same gradual curve from the condyle to the symphysis as in Phascolotherium ; and the condyle, besides being on a lower level, is divided by a less deep notch from the coronoid process. This process is larger in proportion to the entire jaw ; approaches more nearly to the quadrate or rhomboid form, the upper border being less curved ; it affords a more extensive surface of attachment to the principal biting muscles than in most predatory extinct or recent quadrupeds. This character, with the depth and strength of the jaw, suggested the specific name. From the shape of the exposed part of the ramus, we may conclude that the part answering to the angle is bent in wards, and that Triconodon was a genus of the marsupial order. The specimen was discovered by Mr. Beccles in the same " dirt bed" at Purbeck as that in which Spalacotheriton was found.