NATURAL SCIENCES OF PHILADELPHIA. 199 



allies differ ia no important point from those below. It follows, therefore, 

 that the teeth now referred to Auhlysodon, if they belong to the maxillary or 

 mandibular series of Megalosaurus or its allies, could only pertain to the 

 back part. The variation in form of the teeth in question appears too great 

 for such a position. 



The teeth now viewed as characteristic of Aubh/sodon are represented in 

 figs. 36 — 45, pi. ix of vol. xi of the Transactions of the American Philosophi- 

 cal Society. The specimens consist of parts of three teeth, which differ 

 much in size and other important points. In general the crowns are laterally 

 compressed conical, with the anterior part thick and convex transversely as 

 well as longitudinally, and with the sides nearly parallel. The posterior part 

 farms a surface nearly as wide as the thickness of any part of the crown, and 

 is defined from the lateral surfaces at right angles. In the two larger teeth 

 these angles or borders are denticulated, like the trenchant borders of the 

 teeth oi Megalosaurus and its American allies. In the longest tooth (fig. 35, 

 36, op cit.) the posterior surface forms an even plane; in the second sized 

 tooth (figs. 37 — 40) the posterior surface presents a median elevation. In 

 the smallest tooth (figs. 41 — 45), which indeed may belong to a different 

 animal from the preceding, the borders defining the posterior surface are 

 somewhat prominent backward, non-deniiculate, and subside approaching 

 the base of the crown so as to make a transverse section in this position oval 

 (fig. 45). 



Hadrosanrus FouUcii, the bulky vegetable feeder, and cotemporary of the 

 rapacious Lmlaps aquilunguis, was at most probably only specifically distinct 

 from Trachodon mirabilis, the teeth of which were found in association with 

 those of Diiiodon, so that, according to the laws of nomenclatun^, as Trachodon 

 has priority of name, I suppose the first mentioned aninial must be called 

 Trachodon Foidkii. though the names of Uadrosaurus Foulkii and //. mirabilis 

 would appear more appropriate for these powerful dinosaurs. 



The best preserved tooth of those originally referred to Trachodon, repre- 

 sented in figs. 1 — 6 of the plate above cited, is identical in form with those 

 referred to Uadrosaurus, and differs only in the absence of the rugulations of 

 the lateral borders of tfie crown, and in some less important points. 



The remaining specimens of teeth referred with tlie former to Trachodon, 

 are represented in figs. 7 — 20 of the plate cited. Most of them are so worn 

 and probably altered from their original form, that it is rendered uncertain 

 whether ihey belong to the same animal as the preceding tooth, and one 

 unworn (figs. 18 — 20) has a very different shape from this. Perhaps these 

 specimens belonged to another Dinosaur, for which the name Trachodon xn\g\xl 

 be reserved, while that of Uadrosaurus might include the first mentioned and 

 more characteristic tooth. 



As lyuanodonh-xA its enemy in a species of Megalosaurus, Trachodon, the 

 representative of the former both in the western and eastern portions of the 

 North American continent, was accompanied by an equally bloodthirsty 

 enemy, which may, perhaps, on nearer comparison of corresponding parts, 

 prove to be another species of the same genus, until now supposed to be 

 different, under the names of Dinodon and Leiaps. 



Prof. Cope remarks of Lieln.ps (Pr. A. N. S. 1866, 276), that " in its dentition 

 and huge prehensile claws it resembled closely MegalosauruK, but the femuTj 

 resembling in its proximal regions more nearly the Iguanodon, indicated the 

 probable existence of other equally important differences, and its pertinence 

 to another genus." Thus the genus is especially distinguished f>y the appa- 

 rent peculiarity of the femtir, but in my estimation even this disappears if 

 the bone referred to Lxlaps be viewed in the corresponding position to that 

 of M. Bucklandi, represented in pi. vii, pt. iii, of Prof. Uwen's Monograph of 

 the Fossil Reptiles of the Wealden, which appears to me to be the reversed 

 one to that in which Prof Cope has described it in Pr. A. N. S. 1866, 276. 



The teeth oi Bathygnalhus, a huge carnivorous reptile, whose remains have 



1868.] • 



