126 SYSTEMATIC PALEONTOLOGY 



Pleurotoma potomacensis n. sp. 

 Plate XX, Figs. 7, 7a. 



Description. — Shell attenuate, with spire and beak of equal length; 

 aperture narrow; beak long and straight; whorls seven, with four more 

 in the nucleus; few large, raised, revolving lines on and below the shoul- 

 ders; numerous fine, proximate lines between these, and covering the 

 entire whorl; two prominent, raised, revolving lines^ below the suture, 

 the lower more prominent; shoulder with acute nodes, carinated by one 

 or two of the major revolving lines; lines of growth faint. 



Some varieties of P. nasuta Whitfield are very similar to this species. 

 It is intermediate between that species and P. liarrisi Clark. 



Length, 31 mm.; width, 8 mm. 



Occurrence. — Aqitia Formation. 1 mile northeast of Piscataway, 2 

 miles below Potomac Creek. 



Collection. — Mar3dand Geological Survey. 



Pleurotoma ducateli n. sp. 

 Plate XX, Fig. 8. 



Description. — Surface smooth, save for faint, impressed, revolving 

 lines which become stronger just below the suture, and very strong on 

 the beak; suture very distinct; columella straight, striated spirally; lines 

 of growth faint, with broad sinus below the suture. 



Length, 10 mm.; width, 4 mm. 



Occurrence. — Aq.uia Formation. 1 mile southeast of Mason Springs. 



Collection. — Maryland Geological Survey. 



Pleurotoma tysoni n. sp. 

 Plate XX, Fig. 9. 



Description. — Shell eight-whorled; body whorl about half the length 

 of shell; mouth contracting but slightly toward beak; body whorl with 

 sixteen, oblique, longitudinal ribs, strongly nodular where crossed by 

 the large, elevated, revolving lines; eight strong, revolving lines on the 

 body whorl below the shoulder, and numerous fainter ones below, on the 

 beak. All the whorls are concave above the shoulder, and unsculptured, 

 save for lines of growth and for a strong, raised, nodular, subsutural 



