146 SYSTEMATIC PALEONTOLOGY 



dinal ribs visible beneath the tunic; rostrum of the spire elongated and 

 curved; labrum with a prominent angle above." Conrad, 1857. 



Length, 45 mm.; width, 18 mm. 



Occurrence. — ISTanjemgy Foemation. Potomac Creek (Zone 11). 

 Aquia Foemation-. 2 miles below Potomac Creek. 



Collection. — Maryland Geological Survey. 



CaLYPTEAPHOEUS TEINODIFEEUS (?) YAE. 



Plate XXV, Figs. 4, 4a. 



Description. — This form has the prolonged spire and longitudinal rib- 

 bing of C. trinodiferus, differing from it only in lacking the nodes. It 

 might perhaps be referred to a variety of C. velatus, but the characters 

 which separate it from C. velatus seem less likely to be accidental than 

 those separating it from C. trinodiferus. In the Philadelphia Academy 

 of Xatural Sciences are a few specimens of C. velatus which have the 

 prolonged spire of this form, but none have the ribbing on the spire. 



Length, 46 mm.; width, 15 mm. 



Occui'rence. — Xanjemoy Foemation. Popes Creek. Aquia Foema- 

 tign. 1 mile southeast of Mason Springs. 



Collection. — Maryland Geological Survey. 



Family APORRHAIDAE. 



Genus APORRHAIS da Costa. 



Apoeehais potomacensis n. sp. 

 Plate XXV, Figs. 5, 6. 

 Description. — Shell fusiform; spire elevated, pointed; body whorl 

 large; outer lip much expanded; digitations, two, slender and long; pos- 

 terior digitation about tAvice as long as the anterior; callus on the inner 

 lip thick; whorls strongly convex and somewhat angulated below the 

 middle; body whorl with two obtuse revolving ribs, which extend down 

 the middle of the digitations, and disappear in the opposite direction 

 beneath the callus on the labium; about twenty longitudinal ribs on 

 each whorl, with a deep curve below the suture, overridden by fine, 

 raised, close-set, revolving lines. 



