113 



expressed the opinion that the fore-limbs of the Pythortomorpha were natatory. 

 That this view was correct I proved by study of the skeleton of Clidasles pro- 

 python; and it now appears that the fore-limbs of the latter were the first 

 ever described. 



The humerus of the Mississippi Protostega (see Leidy, I. c, PI. viii, 

 Figs. 1-2) is more elongate than that of the P. gigas, is less contracted 

 medially, and the (great trochanter or) deltoid crest is longer and stouter. 

 This I called Protostega tuberosa. 1 (Proceedings of the American Philo- 

 sophical Society for 1872, p. 433.) I also pointed out the existence of a 

 third species, as distinguished by the form of the humerus, in the green- 

 sand of New Jersey, which had been referred by Leidy to the " great 

 MosasaurusP From this specimen, Leidy inferred the natatory character 

 of the limbs of Mosasaurus. The New Jersey species I called Protostega 

 neptunia. A name had been already proposed for it; but, as it was unac- 

 companied with specific or generic description, I did not adopt it. This was 

 done in accordance with the well-known rule that such names without descrip- 

 tion are useless in nomenclature ; and I conceive it to be not only a privilege 

 but a duty to ignore names put forward in this manner. 



The custom of giving generic and specific names without corresponding 

 diagnosis has only recently been introduced, and has no claims to respect. It 

 will, if continued, render the science of paleontology accessible only to a priv- 

 ileged class, who may have control of museums, or who can adopt a nomadic 

 life in traveling from one musem to another. In the case of the Protostega nep- 

 tunia, had Professor Leidy, who figured and described the specimen for the 

 first time, adopted the name already given, I should have felt bound to em- 

 ploy the latter, ascribing it to Leidy as the author; but, as he left it among the 

 synonymy of the Mosasauroids, I have thought it advisable to follow him. 



PYTHONOMORPIIA. 



The characters which distinguish this order are the following: 



1. The quadrate bone is attached to the cranium by a ginglymoid articu- 

 lation, admitting of free movement. 



2. The ribs are attached by simple articulations to single articular facets 

 oi'diopophyscs springing from the bodies of the vertebra?. 



1 I inadvertently wrote 1'latecarjius tubcrosus in the above essay. 



15 c 



