140 SYSTEMATIC PALEONTOLOGY 



tudinal folds, and about fifteen, raised, obtusely rounded, revolving ribs 

 becoming alternate toward tlie base; other whorls with six ribs; lines of 

 growth fine and shar|); outer lip with ten, irregularly spaced teeth; canal 

 short, slightly curved. 



Length, 11 mm.; width, 5 mm. 



Occurrence. — Aquia Foemation. 2 miles below Potomac Creek, Po- 

 tomac Creek, 1 mile southeast of Mason Springs. 



Collection. — Maryland Geological Survey. 



Genus CHRYSODOMUS Swainson. 



Cheysodomus engonatus (Heilprin). 



Plate XXIII, Fig. 6. 



Fusus (Hemifusiis?) engonatus Heilprin, 1880, Proc. Acad. Nat. Sci. Phila., voL 

 XXXV, p. 372, pL XX, fig. 8. 



Description. — " Shell turreted, of about ten volutions, the first three 

 whorls smooth and convex, the remainder strongly carinated, and trans- 

 versed by numerous fine revolving lines, which on the median portion 

 of the body whorl alternate with intermediate finer striae; body whorl 

 impressed immediately below the carination (shoulder angulation); lines 

 of growth sinous, and approximating the characteristic lines of the 

 Pleurotomidae; aperture considerably exceeding the spire in length; 

 columella slightly arcuate, and presenting a rudimentary fold at about 

 its central portion." Heilprin, 1880. 



Length, 33 mm.; width, 16 mm. 



Occurrence. — Aquia Foemation. 2 miles beloAv Potomac Creek, Po- 

 tomac Creek. 



Collections. — Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences. 



Genus PSEUDOLIVA Swainson. 



Pseudoliva sp. 

 Plate XXIII, Fig. 7. 

 Description. — Only internal casts of this form have been found. They 

 are not unlike in size and shape to P. venusta (Conrad), but it is not 

 safe to attempt a specific determination. 



