MARYLAND GEOLOGICAL SURVEY 293 



somewhat elongated, both distinct ; pallial sinus profound, rounded, faint ; 

 exterior semi-polished with faint concentric growth lines discernible; 

 dorsal and posterior slopes meeting in an abrupt curve running from 

 beak to base and becoming less marked near the base. 



Length, 35 mm.; height, 17 mm.; diameter, 3.5 mm. 



Occurrence. — Choptank Formation. Governor Kun, Jones Wharf. 

 Calvert Formation. Plum Point. 



Collection. — Maryland Geological Survey. 



Genus ASAPHIS Modeer. 



AsAPHis centenaria (Conrad). 



Plate LXXI, Figs. 8, 9. 



Petricola centenaria Conrad, 1833, Amer. Jour. Sci., vol. xxiii, p. 341. 



Petricola centenaria Conrad, 1838, Fossils of the Medial Tertiary, p. 17, pi. x, lig. 1. 



rsammocola regia H. C. Lea, 1845, Trans. Amer. Pliilos. Soc, vol. ix, p. 234, pi. 



xxxiv, fig. 17. 

 Psammocola pliocenaTwomey and Holmes, 1856, Pleiocene Fossils of South Carolina, 



p. 91, pi. xxii, fig. 8. 

 Fliorytis centenaria Conrad, 18G3, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 576. 

 Asaphis centenaria Dall, 1900, Trans. Wagner Free Inst. Sci., vol. iii, pt. v, p. 981. 



Description. — " Shell oblong oval, with numerous prominent radiating 

 striae, and concentric wrinkles; lunule small, cordate, profoundly im- 

 pressed ; hinge with two teeth in one valve and three in the opposite, the 

 middle one bifid. Length, two inches." Conrad, 1833. 



Shell somewhat variable in outline and in proportion of length to alti- 

 tude; irregular surface undulations quite marked or almost absent; the 

 fine radial ridges usually somewhat undulating and often more distant on 

 the anterior slope; left valve with but two teeth, the anterior one bifid 

 and bounded anteriorly by a deep socket; a well-marked groove backward 

 from the beak across the posterior hinge area ; pallial sinus profound and 

 rounded anteriorly; shell slightly gaping posteriorly. 



Length, 53 mm. ; height, 35 mm. ; diameter, 10 mm. 



Occurrence. — Choptank Formation. Governor Run, 2 miles south 

 of Governor Run, Flag Pond, St. Leonard Creek, Jones MHiarf, Pawpaw 

 Point, Dover Bridge, Peach Blossom Creek, Greensboro. Calvert For- 

 mation. Fairhaven, Plum Point, Lyon's Creek, Magruder Ferry. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



