MAKYLAM) OK OI.OC IC AL SURVEY 189 



J)cs(ri/ili()ii. — ■■ Shell small, niliiciilar, siil)|)('lhici(l. nearly eqiiilalcral, 

 iliiii; siii'lacc shiiiiiii: wilh line, delicate concentric lines and rather ol)- 

 sciire. in places olisnlcli-, radial I'iljs that show most strongly near the 

 aniciiiir mai-gins; nnihones approximate and acute; auricles very un- 

 (•(|iial and costatcd." (!lai'k, LSi)(i. 



This very lieanliful species shows some points of similarity to I', cal- 

 vatus Conrad in I'oini and surface features, but the radial striae are lack- 

 ing upon the latter. It differs from P. choclavensis in its feebler sculp- 

 ture. It possesses a faint camptonectes structure. 



Width, :i() mm.; height, 18 mm. 



Occurrence. — Nanjemoy Formatiox. AVoodstock, Upper Marlboro 

 (deep cut near Chesapeake Beach E. E. station). Aquia Forma- 

 tion. Potomac Creek, South East Creek (1 mile above Chester Eiver). 



Collections. — Johns Hopkins University, Maryland Geological Survey. 



Pectex johxsoxi Clark. 

 Plate XLIV, Figs. 8, 8a. 



Pecten johnsoni Clark, 1895, Johns Hopkins Univ. Circ, vol. xr, p. 5. 

 Pecteii johnsoni Clark, 1896, Bull. 141, U. S. Geol. Survey, p. S.5, pi. xxxiv, figs. 

 3a, 3&. 



Description. — "Shell small, suborbicular, equilateral; surface Avith 

 about twenty uniform, distant, rounded eostate, separated by broad 

 interspaces, with a few short costae at basal margin, the whole crossed 

 by fine lines of growth; ears prominent, unequal." Clark, 1896. 



P. (jreggi Harris resembles this form very closely. It differs in hav- 

 ing stronger camptonectes structure, and in not having the number of 

 ribs increase toward the periphery. 



Width, 1^ mm.; height, 15 mm. 



Occurrence. — IsTax^jemot Formatiox. 'Woodstock. Aquia Forma- 

 tiox. 2 miles below Potomac Creek, Potomac Creek, Mouth of Paspo- 

 tansa Creek. 



Collections. — Johns Hopkins University, Maryland Geological Survey. 



