No. 2389. FAUNA OF THE MARYLAND ARUNDEL— GILMORE. 591 



where faunal lists have been used to prove the synchronous nature 

 of widely separated formations. 



The contention of Marsh, 30 corroborated by Hatcher, 31 and the 

 later even more positive assertion of Lull 32 that the Arundel fauna 

 "correlates the beds wherein they are found absolutely with the 

 Morrison (Como) of the west," is a conclusion which this recent study 

 shows can not be maintained. 



Forms that have been founded on single teeth or a single bone, 

 especially in the reptilia, do not permit of an accurate diagnosis of 

 that form, and neither does it permit of a satisfactory comparison 

 with other specimens. Some of these, as the types of Coelurus gracilis, 

 Dryptosaurus? medivs, and Dryptosaurus? potens, are certainly deter- 

 minable as to suborder, possibly family, but are not surely deter- 

 minable generically, as the genera of carnivorous dinosaurs are now 

 distinguished. The remaining Theropod, Ornithomimus affinis, is 

 certainly distinguishable as to family, possibly as to genus. 



While the synonymy of the two genera and three species of the 

 Sauropoda found in the Arundel fauna is somewhat uncertain at this 

 time, the materials are entirely sufficient on which to characterize at 

 least one good genus and two species, and for the purposes of the 

 present discussion this appears entirely adequate. 



The Orthopoda is represented by the single genus and species, 

 Priconodon crassits, based on a single tooth. At this time our knowl- 

 edge of the armored dinosauria is such that we do not know whether 

 the teeth are diagnostic of genera or not. Taking into account the 

 highly specialized character of the teeth in the few known forms, it 

 would appear that perhaps in this group of reptiles, when sufficiently 

 well known, it will be found that the teeth are diverse enough in their 

 characters to at once tell to which particular genus they pertain. 



The above review of determined forms shows the evidence for the 

 correlation of the Arundel fauna with the Morrison, rests entirely on 

 the presence of Sauropodous dinosaurs in both formations, and the 

 apparent occurrence of one genus Astrodon (Pleurocoelus) common to 

 both, although a review of the Morrison materials identified as per- 

 taining to Astrodon (Pleurocoelus) by both Marsh and Hatcher is 

 scanty and not altogether reassuring as to the soundness of their 

 identifications. It is my conclusion that, with the exception of 

 Astrodon (Pleurocoelus) , there is not another one of the named dino- 

 saurian specimens from the Arundel which at this time can be said to 

 be closely allied to any of the Morrison forms. 



On the other hand the presence of an Ornithomimid dinosaur per- 

 taining to the family Ornithomimidae, which has never before been 



30 Amer. Journ. Sci., vol. 11, 1896, pp. 43»-436. 



31 Annals Carnegie Museum, vol. 2, 1903, pp. 13-14. 



81 Lower Cretaceous, Geol. Survey of Maryland, 1911, p. 178. 



