NATURAL SCIENCES OF PHILADELPHIA. 197 



condition is estimated to have been 5 inches long. The diameter of the fang 

 is 20 and 21 J lines. 



In the large proportion of cementum to the dentinal axis of the teeth of 

 Iloplocetus they bear such a resemblance to the fragments found in the Red 

 Crag of England, and referred b}' Prof. Owen to a genus under the name of 

 Balxnodoti, as to render it probable the former is the same as the latter. 



Tbe relations of Hoplocetus or Balxnodon, other than that they were toothed 

 cetaceans, are unlinown. 



DeLPHIiNUS oociduos. 



An e-xtinct species is indicated by a fossil derived from the upper miocene 

 formation of Half-moon Bay, California, submitted to my examination by 

 Prof. J. D. Whitney. The specimen consists of an intermediate portion of 

 the upper jaw, devoid of teeth, and encrusted with seleniie. It measures 

 along the more perfect lateral border 5 inches, and in this extent is occupied 

 with 19 closely set, circular alveoli, rather over 2 lines in diameter. At the 

 back of the fragment the jaw has measured a little more than 2 inches wide. 

 From this position it gradually tapers for half its length, and then proceeds 

 with parallel sides to tbe fore end, where it is 10} lines wide. The palate 

 behind is nearly plane or slightly convex; at its fore part it presents a deep 

 median groove, closed by the apposition of the maxillaries, and this groove 

 is separated only by a narrow ridge from the alveoli. The sides of the max- 

 illaries are slightly concave longitudinally, convex transversely. The inter- 

 maxillaries are broken away, leaving a wide, angular gutter between the 

 remains of the maxillaries. 



Remarks on a jaw fragment of MEGALOSATIRTJS. 

 BY JOSEPH LEIDY, M. D. 



A fossil worthy of notice in the Museum of the Academy consists of the 

 fragment of a jaw, apparently of the Megalosaurus, which, if it does not be- 

 long to a different species from 31. BucHandi, indicates an individual larger 

 than any one of those referred to by Buckland, Cuvier, Owen, etc. The fossil 

 was purchased in England, and was presented to the Academy by Dr. Thomas 

 H. Wilson. It is labelled, " Fragment d'une machoire de Megalosaurus trouv6 

 dans le lias ii Boue (or Boues). L'animal est extremement rare ici. II avait 

 45 pied de longeur." In another hand it is marked " Jura Mts." 



The fragment contains two mutilated teeth, visible throughout their length 

 from the inner part of the jaw being broken away. The matrix adhering to 

 the fossil consists of an oolite composed of a homogeneous clay-colored basis, 

 with imbedded granules, of a rounded form, brown and shining. 



The teeth are inserted into the jaw about two-thirds their length, and more 

 than three-fourths the depth of the bone. They have measured 5} and 6 

 inches in length. The breadth at the base of the enamelled crown of the 

 best preserved tooth is 14| lines, which is nearly the fourth of an inch 

 greater than in the largest tooth represented in any of Prof. Owen's figures 

 in his Monograph of the Fossil Reptiles of the Wealden Formation. A tooth 

 apparently nearly as large in an American ally, is one referred to Dinodon 

 horridus, and represented in fig. 21, pi. 9, of my memoir on the Extinct Verte- 

 brata of the Judith River, published in the eleventh volume of the Transac- 

 tions of the American Philosophical Society. The reconstructed outline of 

 this figure is, however, too large, rendered so by the too distant removal of 

 the ap° X of the tooth from the other fragment. The breadth of this specimeu 

 really did not exceed an inch. 



The longe-t tooth of the fossil under inspection, for the most part broken 

 away, exhibits a mould of the large interior pulp cavity. This mould, from 

 the hotiom of the latter to its broken end in the position of the crown, is S^- 



1868.] 



