312 Systematic Paleontology 



This species is represented by a single cast. 

 Length, 6 mm. ; diameter, 4 mm. 



Occurrence. — Arundel Formation, Arlington, Anne Arundel 

 County, Maryland. 



Collection. — Maryland Geological Survey. 



Family VIVIPARIDAE 



Genus VIVIPARUS Montf. 

 ViVIPARUS MARYLANDICUS Sp. UOV. 



Plate XXI, Figs. 1-3 



Description. — Shell subcorneal; sutures deep; whorls flattened; sur- 

 face probably smooth, except for lines of growth ; last whorl much larger 

 than the earlier ones. 



This species is represented by two casts, of which pi. xxi, fig. 1, is 

 regarded as the type. 



Length, 12 mm. ( ?) ; diameter, 7 mm. 



Occurrence. — Arundel Formation. Arlington, Anne Arundel County, 

 Maryland. 



Collection. — Maryland Geological Survey. 



YlVIPARUS vVRLINGTONENSIS Sp. UOV. 



Plate XXI, Figs. 4, 5 



Description. — Shell conical, elongate; sutures moderately deep; 

 whorls slightly flattened; surface apparently smooth, except for lines of 

 growth; whorls four in number, the last whorl larger than earlier ones. 



This species is represented by two specimens which show the whorls 

 in cross-section; pi. xxi, fig. 4, is regarded as the type. 



Length, 11 mm.; diameter, 6 mm. 



Occurrence. — Arundel Formation. Arlington, Anne Arundel County, 

 Maryland. 



Collection. — Maryland Geological Survey. 



