406 Systematic Paleontology 



AvELLAXA PINGUIS n. Sp. 



Plate XVIII, Figs. 5, 6 



Description. — Shell moderately large for the genus, ovate and squat in 

 outline ; whorls broadly rounded, increasing rather rapidly in size, approxi- 

 mately six in number; apex broken away so that exact number is inde- 

 terminate and apical characters are lost ; external surface sculptured with 

 feebly impressed linear sulci, eight or nine in number upon the penultima, 

 eighteen or twenty upon the ultima; suture lines distinct, impressed; 

 aperture rather narrow, pyriform; outer lip imperfect, feebly arcuate, 

 apparently, and slightly patulous anteriorly ; inner lip heavily reinforced, 

 bearing near its anterior extremity two strongly elevated, oblique plica- 

 tions and half-way between them and the posterior commissure a third 

 prominent plication set normal to the columella; parietal wall thickly 

 calloused from the posterior commissure to the anterior emargination, 

 the outer margin of the wash parallel to the outer lip posteriorly, expand- 

 ing near the horizontal fold ; anterior notch moderately deep. 



Dimensions. — Altitude 11.8 mm., maximum diameter 9.8 mm. 



This species is most readily separable from A. lintoni n. sp. by the much 

 more numerous spiral lirations. From A. costata (Johnson) it is dis- 

 tinguished not only by its larger size, but also by its stouter and more 

 rounded outline. It is rare even at the single locality at which it is repre- 

 sented. 



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

 County. 



Collection. — Maryland Geological Survey. 



AVELLANA LINTONI n. Sp. 



Plate XVIII, Fig. 1 

 Description. — Shell rather stout, ovate, scalariform in outline in the 

 cast; whorls five or six in number, narrowly tabulated posteriorly in the 

 cast, those of the spire straight-sided, the body whorl evenly but feebly 

 inflated, abruptly constricted at the base; external surface decorticated, 

 leaving no trace of sculpture excepting at the labial varix; suture lines 



