]\[Ar{Yi.AND Geological Survey 609 



Anterior end short, regularly rounded. A-'alves regularly convex in the 

 lower and posterior portion, becoming gibbous in the middle and above. 

 BeaJcs at about the anterior third or fourth, rather prominent. Umbonal 

 slope subangular above, and sometimes continued to the postinferior 

 extremity. Cincture broad, undefined, extending from the beaks to the 

 base anterior to the middle, and producing a flattening of the valve and 

 a slight constriction of the basal margin. Surface marked by fine con- 

 centric striae, Avith a few, more or less distinct, concentric undulations, 

 which become obsolete at about the umbonal angle. Interior unknown. 

 This species resembles G. communis, but the concentric undulations are 

 not so numerous, the umbonal slope less defined, the posterior end broader 

 and not so obliquely truncate above the middle, and the cincture more 

 nearly vertical." Hall, ISS-"). 



A few poorly preserved specimens have been observed which seem 

 probably referable to the species. 



Length 21-30 mm.; height 14-21 mm. 



Occtirrence — Jennings Formation, Chejviung Member. Town 

 Creek, 3870. 



Collection. — Maryland Geological Survey. 



Genus PAL/^ANATINA Hall 

 PAL.EANATINA ANGDSTA Hall 



Plate LIX, Figs. 16, 17 



Palaantina angusta Hall, 1885, Pal. of N. Y., vol. v, pt. i, li, p. 490, pi. Ixxix, 

 figs. 29-34. 



Description. — " Shell small, elongate, narrowly elliptical or subcylin- 

 drical ; length from two and a half to three times the height ; basal margin 

 straight or slightly sinuate. Posterior extremity obliquely truncate or 

 regularly rounded. Cardinal line straight or slightly declining poster- 

 iorly. Anterior end narrow, rounded. Left valve gibbous in the umbonal 

 region. Eight valve less gibbous and more depressed below the umbonal 

 ridge. Beaks between tlie anterior third and fourth, small, scarcely 

 rising above the hinge. Umbonal slope obtusely subangular, extend- 

 ing to the postinferior extremity. Postcardinal slope flat or con- 

 39 



