Maryland Geological Survey 421 



Superfamily RACHIGLOSSA 



Family OLIVIDAE 



Genus OLIVbLLA Swainson 



[Zool., 111., vol. ii, 1831, pi. lviii] 



Type . — Olivella danea Mawe. 



Small polished, cylindrical shells, produced into tapering spires; aper- 

 ture narrow posteriorly, dilated forward ; outer lip simple, sharp ; inner 

 lip calloused near the suture, obliquely plicate forward. 



The Olivella are separated from the Olives by the smaller size of the 

 former, the less oblique, more shallow basal notch, the higher spire and, 

 in the recent shells, by the presence of an operculum. 



Olivella monmouthensis n. sp. 

 Plate XIV, Fig. 10 



Description. — Shell heavy, rather large for the genus; slender, fusi- 

 form in outline, the maximum diameter falling near the limit of the ante- 

 rior third ; apex of spire broken away and number of whorls and nuclear 

 characters lost; external surface smooth, polished, suture lines glazed 

 over; aperture narrow, lenticular, outer lip broadly and symmetrically 

 arcuate; inner lip smoothly concave; anterior canal short and straight 

 with subparallel margins ; parietal wall glazed, its outer margin apparently 

 not well defined, an obtuse fold visible, however, sweeping in a gentle curve 

 from the medial portion of the parietal wall to the anterior extremity of 

 the outer lip ; anterior canal emarginate in front. 



Dimensions (imperfect individual). — Altitude 15 mm., maximum 

 diameter 7 mm. 



This species is not confusable with any described form from the Upper 

 Cretaceous. 



Occurrence. — Monmouth Formation. Brightseat, Prince George's 

 County. 



Collection. — Maryland Geological Survey. 



Etymology: Olivella, little olive. 



