432 Systematic Paleontology 



Occurrence. — Monmouth Formation. Brightseat, Brooks estate near 

 Seat Pleasant, Friendly and McNeys Corners, Prince George's County. 



Collection. — Maryland Geological Survey. 



Outside Distribution. — Ripley Formation. Exogyra costata zone. Owl 

 Creek, Tippah County, Mississippi. 



Liopeplum monmodthense n. sp. 

 Plate XV, Figs. 6, 7 



Description. — Shell thin, highly polished, slender, fusiform in outline, 

 the maximum diameter falling a little in front of the medial horizontal ; 

 whorls probably seven or eight in number, converging at an angle of 20° 

 to 25°, flattened dorso-ventrally, the later volutions closely appressed and 

 constricted directly in front of the suture, the body whorl broadly arcuate, 

 smoothly rounded at the base and merging gradually into the broad pillar ; 

 early whorls of the spire sculptured with short, broadly rounded, retractive 

 riblets, approximately ten to the whorl and restricted to the posterior half ; 

 incremental sculpture strongly developed on the appressed portion of the 

 later whorls but no true costae ; spiral sculpture absent altogether ; 

 aperture narrow, elliptical; outer lip thin, sharp, broadly arcuate; inner 

 lip smoothly concave at the base of the body ; columellar plications three 

 in number, the two posterior folds very feeble and evanescing before reach- 

 ing the aperture, the anterior fold quite strongly elevated, twisted and 

 thickened at the margin of the aperture and running parallel to the colu- 

 mella for about 3 mm. before its final evanescence ; pillar imperfect, but 

 probably broad and not very long, with rather distant parallel margins. 



Dimensions (imperfect individual). — Altitude 47 mm., maximum 

 diameter 22 mm. 



This species is more evenly rounded and more regularly fusiform in 

 outline than any other member of the genus reported from Maryland. 



Occurrence. — Monmouth Formation. One mile west of Friendly. 

 Prince George's County. 



Collection. — Maryland Geological Survey. 



