FROM THE PURBECK OOLITE. 649 



Several other jaws -with, similar tricuspid teeth of larger dimensions, 

 found by Mr. Beckles, indicate the existence of another species of Tri- 

 conodon of a more elongated form, and about one-third larger in size. 

 From one of these the following evidence of its marsupial character was 

 pointed out to me by Dr. Falconer. 1. The plurality of true molars. 

 2. The strong, inflected angular process. 3. (And this is considered 

 by him the most significant of all), the broad, salient, everted rim of 

 the ridge which is decurrent on the outer side from the condyle along 

 the inferior margin, exactly as in the carnivorous marsupials. 4. The 

 marked development of the mylo-hyoid groove. He also adds, that 

 these two species of Triconodon, from the cutting character of their 

 teeth, and their comparatively formidable canines, together with the 

 form of the ascending ramus, are more like small ferine animals than 

 mere insectivorous marsupials. It is most probable that they fed on 

 prey less minute than insects. 



Among the jaws of many smaller insectivora is one allied to the type 

 of the Stonesfield Amphitherium, but generally distinct.* 



The following observations by Professor Owen, on the genus Tri- 

 conodon, extracted from a letter which I received from him January 27, 

 1857, are not the less interesting as having been written before tha> 

 more decisive proofs above enumerated of the marsupial characters of 

 Triconodon had been elicited from more perfect specimens obtained 

 about a month later : — " The Purbeck fossil (the smaller Triconodon) 

 is most nearly allied to the Stonesfield insectivorous genera, and shows 

 characters intermediate between Phascolotherium and Thylacotherium. 

 The three-coned tooth presents the same type as in the molars of 

 these genera, but the first and third cones are developed to nearer 

 equality with the second or mid-cone. The cingulum in Triconodon 

 develops the same front and back talon. In the size of the canine, 

 and in the depth and other proportions of the jaw, Triconodon resem- 

 bles Phascolotherium, and so much so in the jaw-bone characters that 

 if one be marsupial the other should be ; but I cannot get a clear 

 evidence of the inward bend of the angle, or of its extension back- 

 wards. 



"In the superior number of molars, Triconodon resembles Thyla- 

 cotherium, and also Myrmecobius, which, by the way, has a somewhat 

 similar type of molar tooth. The above-cited genera and Spalacothe- 

 rium have enough of characters in common, so far as regards mandible 

 and mandibular teeth, to suggest their all belonging to the same natural 



of them three subequal sharp-pointed cusps, rising nearly vertically into the 

 same longitudinal plane, with basal end lobules, but without additional interior 

 complication. They are so arranged, in a continuous and compact series, as to 

 present a uniform serrated edge, like the teeth of a saw. — Dr. Falconer. 



3 In this species the lower jaw has an elongated slender ramus, containing 7 

 uniform back molars in situ, and the empty alveoli of 4 or 5 false molars in 

 front, together with a prominent laniariform tooth. The dental formula agrees 

 numerically with that of the Amphitherium, but differs from it in the double- 

 rowed and complex arrangement of the crown-cusps. — Dr. Falconer. 



