Omitliosaurian Genus Oniitlioclielras. 533 



characters found amongst this medley of bones and those of 

 the pterodactyls of the Chalk of Kansas. Its effect is seen 

 when Professor Williston ^ remarks that "every essential 

 character tliat has been given so far for the European species 

 of this group agrees quite ^vith those of our Kansas speci- 

 mens. This will demonstrate how unimportant are the 

 characters derived from the absence or presence of teeth." 



In the present case the absence or presence of teeth affords 

 a certain character, although amongst Icthyosaurs and Aves 

 it has been shown to be not dependable. Therefore it would 

 be extremely unwise to follow this rule too closely, for a 

 toothed condition is a more primitive character in this 

 respect than a toothless. We must make use of the features 

 we have at command when dealing with such fragmentary 

 remains. Moreover, at the time of the deposition of the 

 Cambridge Greensand they were an expiring race and near 

 the end of their line, and thus we are examining the fixed or 

 degraded characters of the ultimate descendants, and not the 

 ancestors. Therefore the peculiarities obtaining have a 

 greater value than if found in the beginners, for they are 

 the specialized result of natural selection acting through 

 ages. The situation of the front pair of teeth in some jaws, 

 right above the palate on the anterior face of the bealc, we 

 shall shortly show is an accident caused by the wearing 

 away of the snout. Those without teeth must for a great 

 period have diverged from those with teeth. The fact that 

 the seizure and prehension of food are obtained by such 

 opposite means argues of itself corresponding variations in 

 the form of the bones of the skull. In the Cambridge 

 material many of the teeth are grooved and cii'cular, and 

 certainly more simple and less specialized than the remainder, 

 which ace more or less compressed laterally, with an absence 

 of grooving. To conclude that the odd bones belonged to 

 the same individuals, or even to the identical genus, as the 

 fragments of skulls, because they happen to be found on the 

 same horizon, is a dangerous means of diagnosis, and has not 

 infrequently led to error in the past. This danger is inten- 

 sified when we remember that the Cambridge Greensand is 

 the remains of an old shore-line, Avhere bones of these 

 creatures accumulated, not only from those contemporaneous, 

 but also probably from those derived from older l)eds, and 

 could not have formed even a tithe of the flocks of these 

 reptiles inhabiting the district. 



* S. W. Williston, " Restoration of Ornif/iostoma,'' Kansas Quartcrlv, 

 1897, p. 35. 



