300 PROCEEDINGfi OF THE NATIONAL MUSEUM. vol. xxxvi. 



The finding of C anvptosaarus remains in the Lakota, near Buffalo 

 Gap, South Dakota, a^^pears to extend the geological horizon of this 

 genus. The occurrence of these fossils is described by Mr. N. H. 

 Darton*^ as follows: 



The formation lias yielded a large number of cycads, notably those described 

 by Mr. Lester F. Ward. These and associated plants are regarded by Mr. 

 Ward as Cretaceous in age. In 1898 I discovered saurian bones in or near 

 the cycad horizon at Buffalo Gap, but as they are of new species it is difficult 

 to obtaiu from them any evidence bearing on the age of the formation. If it 

 were not for the evidence of the flora, these bones would be regarded as late 

 Jurassic in age. * * * rpj^g bone bearing beds are in the middle of the 

 Lakota formation, or about 90 feet above the unconformity on the Unkpapa 

 sandstone which is approximately the horizon that has yielded the cycads 

 between Edgemont and Minnekata, near Blackhawk and elsewhere about the 

 hills. 



The vertebrate fauna of the above horizon, as now known, con- 

 sists of Iloplitosaurus {Stegosuurus) marshi (Lucas) and Camp- 

 tosaurus depressus, new species, while the presence of a sauropodous 

 dinosaur is indicated by some fragmentary bones found associated 

 with the type material. 



That the bone-bearing layer at Buffalo Gap is later than the fossil 

 horizon in Quarry 13, Como, Wyoming, appears quite probable, al- 

 though the evidence as yet is insufficient to conclusively establish the 

 fact. IIoplitosaKnis has its nearest ally in Polocanthus of tlie AVeal- 

 den. While the former genus is known by a single fragmentary speci- 

 men only, it may, from its geological position, rei)resent a forui in- 

 termediate between Stegosmvnis of the Jurassic, and Nodosaurus^ 

 Stegopelta, and Anchylosaurus of the American Tapper Cretaceous. 



Although the typical specimen of C. depressus is fragmentary, 

 such parts as are preserved appear to show that of all the known 

 forms of Camptosaurus this species approaches the Wealden Igua- 

 nodon most closely, as indicated by the narrowness of the ilium and 

 the coosification of the sacral vertebrae. 



As has been pointed out in the preceding pages, the G cmiptosauriis 

 remains from Quarry 13, wdien compared with Iguanodon., show a 

 more generalized structure, which suggests a somewhat greater an- 

 tiquity for the beds in which they are found. In this connection it 

 is a significant fact that of the several European species referred to 

 C aTThptosaurus^ the only valid one is G . prestwichii from the Kim- 

 meridge Clay, and its affinities appear to be nearest to G . nanns, the 

 holotype of which was found in Quarry 13. Corroborative evidence 

 is furnished b}^ the abundant remains of Stegosaurus found in the 

 above quarry (see Plate 6), which genus is so closely allied to Dacen- 



"21st Ann. Rept. U. S. Geol. Surv., Pt. 4, 1§99-1900, p. 527. 



