AND AVES OF NOUT1I AMERICA. 



117 



II' Dr. Leidy had left the matter undecided as to which of these he regarded as the type of the semis Dinodon, 

 the almost universal practice of naturalists would refer the name to that form which should not be first thereafter 

 discovered to be distinct, and named. 



i have been of the opinion that the two forms of teeth included by Leidy under the head of Dinodon really belong 

 to distinct animals, and Leidy is also of that opinion. Tn 1866, in describing the genus Laelaps (Proc. Acad., p. 279), 

 I said, " The genus Laelaps belongs to the family Dinodontidae which is characterized, * * by its compressed, 

 sabre-shaped teeth. It, differs * * from Dinodon in that teeth of the latter have two posterior serrate edges 

 separated by a posterior plane." This, then, according to the usage of naturalists establishes the name Dinodon for 

 the trunoate teeth and Laelaps for the two-edged. 



Dr. Leidy however in an essay published in Proo. Academy Nat. Sci., 1868, p. 198, in expressing Ids belief in the 

 distinctness of the two genera, states that " teeth of like shape " (i. e*. like Megalosaurus) referred by me to Dinodon 

 alone, belong to this genus, and names the species represented by the truncate teeth, or the true Dinodon horridus, 

 Aublysodon mirandus. lie then goes on to say, "Future discovery may prove Laelaps and Dinodon identical," and 

 on p. 199 * * "An enemy which may perhaps on nearer comparison of corresponding parts prove to be 

 another speoies of the same genus until now supposed to be different, under the names of Dinodon and Laelaps." 

 It is thus sufficiently obvious that the proposition is to refer Laelaps as a synonyrne of Dinodon. It appears to me, 

 on the other hand, that this is contrary to the rules of nomenclature, and the principles which lie at their root,, and 

 that the name Aublysodon is a, synonyrne of Dinodon. 



This ishowever on the supposition that Leidy bad left the question open or uncertain, as to which of the two 

 forms of teeth was characteristic of his genus Dinodon. I think however he has not left it undecided, and 1 am 

 supported in this by the opinion of Von Meyer. 



The teeth of Laelaps both from New Jersey and Nebraska do not, differ from those of Megalosaurus, while those 



ofDinod lo. itwasnottobe supposed that Dinodon was established on teeth of the former character, as the 



practice of describing species and genera, without a basis of distinctive characters is an unusual and bad one, and 

 ought not to be tolerated in natural science. 



In describing Dinodon, Leidy says the Laelaps-like teeth resemble those of Megalosaurus, and in his reoent 

 article in the Proo. Academy (p. 198), that they are "identical in character with those of Megalosaurus." 



lie moreover specifies that the truncate teeth of Dinodon are really those that characterize it, in the following 

 words: "as the entire; dent, it, ion of Megalosaurus has not yet been ascertained, it may turn out to be the case that in 

 other parts of the jaws than those known, it, possesses teeth like the ones above deseribed as peculiar. Should on 

 future discovery such a condition of things be proved to exist, Dinodon would then cease to be anything more than a 

 second species of Megalosaurus." The truncate teeth are, then the "peculiar" feature of Dinodon, and all that 

 prevents the species from being referred to Megalosaurus. 



Von Meyer has understood this language as I have, and has believed that the tooth now ascribed by Leidy to 

 AuUysodon are really characteristic of Dinodon. He says (Palreontographica, vii, p. 267) that some of the teeth 

 " indicate such peculiarity, that Leidy, who has made the investigation, thought it necessary to characterize the 

 animal as distinct, from Megalosaurus, under the name of Dinodon horri d u s . 



If is therefore evident that the Laelaps-like teeth described under Dinodon, are really those that require a new 

 name, if any. I will not give them a name however, since there is no evidence that they differ from either Megalo- 

 saurus or Laelaps, though of course the probability is, that they belong to a species of I lie latter genus. 



Although Aublysodon would thus be a synonyrne of Dinodon, it is not an altogether useless name, since the 

 latter was given years ago to a genus of serpents by Dumerll and Iiihron, and may therefore be suppressed. 



The classification and characters here employed in treating of the Dinosauria, were embraced in the original 

 essay included in the present one, which was read, and the contents communicated verbally, before the Academy of 

 Natural Sciences in the spring of 1867. 



This point is alluded to partly because the portion of the original essay on the Dinosauria has been in part 



anticipated by the publication of a lecture by Prof. T. IT. Huxley before the Royal Society of Great, Britain, bearing 



dale February 7, L868. The tenor and result, of the studies of Prof. Huxley were the same that followed my own, and 



the details of his reasoning arc thus published prior to mine. The position of the ischia and pubes in the Dinosauria, 



AMERF. PHILOSO. 800 VOL. XIV. 30 



