294 PROCEEDINGS OF THE ACADEMY OF [1888.. 



whether the anterior cusp is a cingule or a true paracoue. The 

 posterior cusp or metAcone is prominent and distinct as in the pre- 

 molars of Tricoiiodon. The chief interest lies in the main cusp which 

 is loftier and more pointed than the protocone of the tJiird tooth 

 Avhich in turn has all the characteristics of a molar. This is an 

 important point which has been overlooked previously, since it ap- 

 pears to indicate an available line of division in the functional 

 adaptation of the series, i. e. a line between premolar and molariform 

 teeth. If such a division be confirmed by further examination of the 

 first and second teeth, it will lessen the gap between Amphilestes and 

 this genus and remove what has been considered an entirely excep- 

 tional feature, viz. a type with no premolariform teeth. The mandib- 

 ular formula may then be provisionally written thus: %, Ci, p.,, 



The crowns of this front pair of teeth have never been correctly 

 represented. The writer's figure (op. cit., PI. 8, fig. 3) is incorrect 

 in restoring the cingulum of the second tooth and the basal cusps 

 of the first tooth. In this Buckland's figure was followed, believing 

 it probable that the jaw was in better condition when he figured it 

 than now, for the last molar was then present. Another error in 

 the drawing is the high position of the dental foramen, to wliich 

 Professor Marsh kindly directed attention. 



AMPHITYLUS.' 



In the type of this genus at Oxford the teeth are so fractured that 

 it is impossible to form any idea of their full structure. There is 

 some doubt whether the deutal formula, ("4, Cj, ^4, m-, as gener- 

 ally given, is correct; one cannot be positive, for the 4th and 5th post- 

 canine teeth are much mutilated; the characters of the condyle and 

 angle, however, separate this specimen clearly from Amphilestes. 

 At the time this genus was jiroposed the writer supposed we had in 

 No. 36822 (Brit. Mus. Coll.) a ramus showing the outer face of 

 the Amphitherium molars, but this ])roves to have been a mistake. 

 The crowns of the last three molars in Amphifylus show a jjromi- 

 nent posterior or tliird cusp, of wliich there is no evidence upon the 

 molars o^ Amphitherinm, as seen upon the inner face. The penulti- 

 mate and ante-penultimate molars also retain this third cus)). The 

 fourth, fifth and sixth molars counting from the last, show the trifid 

 division of the crown characteristic of the tric(modont type, then 

 follow the tAvo mutilated teeth with bifid crowns which may represent 

 either premolars or molars. Thus the formula may read either 



1 Proc. Acad. Nat. Sc. Phila. June 21, IS87. 



