No. 2389. FAUNA OF THE MARYLAND ARUNDEL— GILM ORE. 587 



In the parallel columns below the Theropod nature of the cotypes 

 are clearly demonstrated by contrasting their important structural 

 features with the homologous bones of the Orthopod hind foot. 



Theropod characteristics of the cotypes of 



Omithomimvs ojfniis. Characteristics of the Orthopod pts. 



1. Astragalus with ascending process. 1. Ascending process always al sent. 



2. Astragalus narrow fore and aft as com- 2. Astragalus wide fore and aft, as com - 

 pared with transverse diameter. pared with transverse diameter. 



3. Articular surface on distal end of 3. Extent of articular surface on front 

 metatarsal III, extending higher on front and back of distal end of metatarsal III, 

 than on back of bone. sul. equal. 



4. Unguals of hind feet compressed. 4. Unguals of hind feet depressed. 



5. Lateral pits on distal ends of foot 5. Lateral pits on distal ends of foot 

 bones deep and their borders well defined, bones shallow or wanting, their bordois 



when present, illy defined. 



6. Articular ends of foot bones, having 6. Articular end of foot bones, usually 

 well finished surfaces. lacking refinement of their surfaces. 



The Ornithomimid character of these cotypes was established by a 

 direct comparison with the foot bones of the fine skeleton of Orni- 

 ihomimus (Struthiomimus) alius Lambe and other Ornithomimid 

 materials in the American Museum of Natural History, New York. 

 In every instance such close resemblances were found as to leave 

 little doubt of their generic identity. 



For the present purposes it is thought the similarities of these 

 bones may be most clearly demonstrated by showing homologous 

 bones of the Arundel and Belly River Ornithomimids side by side. 

 In plates 112 and 113 are thus illustrated a number of these bones 

 reproduced here from photographs. Their close similarities, in some 

 instances, down to the minutest details appears to me to be sufficient 

 to demonstrate their pertaining to animals of congeneric relationship. 



SAUROPODOUS DINOSAURS. 



Prof. R. S. Lull has given such a thorough and detailed discussion 20 

 of the Sauropod Dinosaur remains from the Arundel formation that 

 for the present purposes a detailed discussion of them appears un- 

 necessary. After a thorough examination of the materials I fully 

 concur in his conclusions. Lull recognized three species of Sauro- 

 podous dinosaurs from the Arundel Astrodon johnstoni, Pleurocoelus 

 nanus, and P. altus. Hatcher contended 21 that — 



Since these remains were found in essentially and perhaps identically the same 

 locality and horizon, and, in consideration of the very great similarity which they 

 exhibit, there appears no good reason for considering them as pertaining to either 

 different genera or species. Astrodon johnstoni Leidy, having priority, should, there- 

 fore, be retained, while Pleurocoelus nanus would become a synonym of that genus 

 and species. 



20 Lower Cretaceous, Md. Geol. Survey, 1911, pp. 188-204. 

 51 Annals Carne. ie Museum, vol. 2, 1903, pp. 11-12. 



