Dr. C. W. Andrews — A New Species of Tetrahelodon. 347 



III. — Note on the Mandible of a New Species of Tetmabelodon 

 FROM THE Loup Fork Beds of Kansas. 



By C. W. Andrews, D.Sc, F.R.S., British Museum (Nat. Hist.).i 



A CONSIDERABLE number of species of Tetrabelodont Mastodons 

 x\. are already known from various horizons and localities in the 

 United States. Several of these from the Loup Fork deposits have 

 been described by Cope,'-^ the best known being Tetrahelodon euhypliodon, 

 T. catnpes/er, and T. productus. A fairly complete mandible recently 

 acquired by the British Museum seems to indicate that yet another 

 very distinct form existed contemporaneously with those just mentioned. 

 This specimen, which forms the subject of the present note, was 

 obtained from Mr. Sternberg, the well - known collector of fossil 

 Vertebrates, who refers to it in his recently published work The Life 

 of a Fossil Hunter (p. 123) under the name Trilophodon campester, 

 Cope, from which, in spite of some similarity, I believe it to be very 

 distinct. 



The mandible, which I propose to make the type of a new species, 

 Tetrahelodon dinotherioides, is from the Loup Fork Beds of North- 

 Western Kansas. It is not quite complete, the upper portion of the 

 ascending ramus being wanting on the left side, while on the right 

 the articular condyle is much worn. The symphysial region also is 

 imperfect, the outer walls of the sockets of the great lower tusks 

 being broken away, while the extremity also is missing, the symphysis 

 when complete probably having been considerably longer. The most 

 striking character of this mandible is the great length and massiveness 

 of the symphysial region (Figs. A, B), which, moreover, is deflected 

 to a greater extent than is the case in any other Tetrahelodon, 

 though considerably less so than in Binotherium. The spout-like 

 upper surface of the symphysis is narrow and deep posteriorly, its 

 concavity being about a semicircle ; in this region its alveolar edges 

 are comparatively thin and sharp. Anteriorly this surface widens 

 out, its concavity is less marked, and its borders become thickened 

 and rounded. As will be seen from the figures and the table of 

 measurements, the whole symphysial region was very massively 

 developed, and the lower tusks, which perhaps were decurved as in 

 Dinotherium, must have been very large, the vertical diameter of 

 their roots being about 11cm., rather greater than the width from 

 side to side. The mandibular rami are very thick from within outwards, 

 and are deepest just behind the symphysis. Their outer and ventral 

 surfaces are strongly convex transversely. The ventral border 

 is concave from before backwards just behind the symphysis, but 

 farther back becomes strongly convex, passing into the hinder border 

 of the ascending ramus : in fact, the whole posterior and ventral 

 outline of the mandible seen in profile is a sigmoid curve. The 

 condyle is not well preserved on either side ; it rises about 23 cm. 

 above the upper surface of the molars. Between the condyle and the 



• Published by permission of the Trustees of the British Museum. 



2 Cope, "The Proboscidea " : American Naturalini, 1889, vol. xxiii, p. 291. 



