Hatcher : Astrodon in U'vo.mixg. 11 



A careful comparison of these remains with those figured by Marsh 

 as pertaining to P/cttroar/iis nanus, based on material discovered by 

 the present writer in the Potomac beds of Maryland, will, I think, show 

 it to be (juite impossible to definitely distinguish these remains either 

 generically or specifically from the latter. The same may be said of 



5 ^6 



Figs. 5 and 6. Lateral and superior views of centrum of distal caudal. (No. 

 585.) One half natural size. 



the material upon which was based Marsh's description oi Plcuroccelus 

 montaniis. These western forms may, however, be specifically distinct 

 from the Maryland species. 



Synonymy of Pleuroccelus nanus Marsh and Astrodon 



JOHNSTONI LeIDY. 



It now remains to discuss the synonymy of the above-mentioned 

 genera and species. 



The generic name of Astrodon was given without description in the 

 American Journal of Dental Science, 1859, by Dr. Christopher Johns- 

 ton to certain reptilian teeth obtained by a Mr. Tyson from a bed of 

 iron ore near Bladensburg, Maryland. 



In 1^6'^,' as, Astrodon Jo/mstoni, Dr. Leidy fully described and fig- 

 ured these teeth, thus placing the genus on a valid foundation. A 

 comparison of Dr. Leidy' s figures of the teeth of Astrodon johnstoni 

 with Marsh's figures of Pleurocadus nanus will show a very striking 

 similarity between the two, which is rendered all the more striking by 

 an actual comparison of the s}>ecimens themselves. Moreover since I 

 myself collected all of the material described and figured by Professor 

 Marsh I can assert that it likewise was found in a bed of iron ore near 

 Bladensburg, Maryland. The exact locality of the Marsh material was 

 certain iron ore mines on the farm of Mr. Wm. Coffin, and especially 

 in that one locally known as " Swampoodle " and situated about one 

 and one half miles northeast of Beltsville on the Baltimore and Ohio 

 Railway, some thirteen miles from \\'ashington. Since these remains 



^ Memoir on the extinct Reptiles of the Cretaceous formations of the United States, 

 Smith, Contr. to Knowl., Vol. 14, PI. XIII, figs. 20-23. 



