156 SYSTEMATIC PALEONTOLOGY 



Genus ODOSTOMIA Fleming. 



Odostomia teapaquaea (Harris). 



Plate XXIX, Fig. 3. 



Syryiola trapaquara Harris, 1895, Proc. Acad. Nat. Sci. Phila., voL xlvii, p. 77, pL viii, 

 flg. 10. 



Description. — " Size and general form as indicated by the figure; 

 whorls 7; 1 small, sinistral; 2-7 polished, slightly tumid, with a well- 

 marked suture; aperture moderate, striate Avithin; one strong plait on 

 the columella." Harris, 1895. 



This species has some resemblance to the figure of Acteon melanellus 

 Lea, but it tapers more gradually, has shorter whorls, stronger lines of 

 growth and no revolving lines (or almost none), while they are strong in 

 A. melanellus. 



Our specimens are very different from the Chiekasawan form — 0. in- 

 significa Aldrich, which Harris regards as a synonym of 0. trapaquara. 



Length, 7 mm.; width, 2.5 mm. 



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

 tomac Creek, Upper Marlboro. 



Collection. — Maryland Geological Survey. 



Family EULIMIDAE. 



Genus NISO Risso. 



ISTiso umbilicata (Lea). 

 Plate XXIX, Fig. 4. 



Pasithea umbilicata Lea, 1833, Contrib. to GeoL, p. 103, pL iv, fig. 85. 



Description. — " Shell elevated above, rounded below, subcarinate, pol- 

 ished; substance of the shell thin; apex acute; suture linear; umbilicus 

 large; whorls nine, flattened; mouth subovate, acutely angular above, 

 one-fifth the length of the shell; columella incurved at base; margin en- 

 tire. ... Its umbilicus is wide, with a large spiral groove. On some 

 of the whorls the line of growth may be indistinctly seen." Lea, 1833. 



Length, 24 mm.; width, 5 mm. 



Occurrence. — Aquia Foemation. Potomac Creek. 



Collection. — Maryland Geological Survey. 



