Maryland Geological Survey 211 



"Quarry 9/' Como, Wyoming (Morrison), preserved in the Yale Mu- 

 seum, which agree in size with those of the type specimen of Goniopholis 

 (Diplosaurus) felix (Marsh). Unfortunately, none of the crowns in the 

 last specimen show their outer surface, but those of the Maryland speci- 

 men differ from those from Como by having secondary ridges between 

 the main ridges on the proximal portion of the crown. See figure. The 

 similarity aside from this feature is very great and shows a close rela- 

 tionship with the Morrison type as the specific name implies. The 

 sculpturing on the scute (No. 5465) is coarser than on any of those in 

 the lot of material from Como. This may, however, be due to the por- 

 tion of the body from which the scute came, and is probably not of 

 importance. 



Tooth No. 8175, M. G. S., may be taken as the type. 



Length of crown about 25 mm. 



Width of crown at base 12 mm. 



Occurrence. — Arundel Formation. Branchville, Prince George's 

 County. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



MOLLUSCA 



Class GASTROPODA 



Order CTENOBRANCHIATA 



Suborder PLATYPODA 



Superfamily TAENIOGLOSSA 



Family AMNICOLIDAE 



Genus BYTHINIA Leach 



Bythinia ardndelensis sp. nov. 



Plate XXI, Fig. 6 



Description. — Shell small, turbinate; sutures pronounced; whorls in- 

 flated, the last much larger than the earlier ones; surface apparently 

 smooth, except for lines of growth. 



