MAini.WI) (M'OI.OCIf'AI, sritVKY 191 



Ostrea coiiipressiroitlnt Harris, 1H'.)4, Aiiier. Jour. Sti., ser. iti, vol. xlvll, p. 302. 

 Ostrea comprcssirniitra Clark, 180.'), Johns Ilojikins I'lilv. Clrc, vol. xv, p. .'j. 

 Ostrea compremiiroxfra Clark, IS'Ki, Hull. 141, I'. S. (Jeol. Survey, j). 8f5, pi. xxxvii, 

 titrs. 1, 2(i-2r\ ])!. xxxviii, lljj;s. \ii, \h, 2a-2r\ \,]. .\xxix, ll^'s. 1, 2a, 2h: \>\. xl, 



li--. 1. 

 Ustriii tiiitt/iressiroslra Dull, iS'.tH, Trans. Watjuer Free lust. Sci., vol. ill, pt. iv, 



p. or'.t. 



Descripliun. — '' Slicll siiiishnl, siilniMitc: iujrr'uir niirr (Miiivcx. with 

 luiiiicnuis (■(in\('\ I'ilis iiitci-rii|iic(| hy r(ii-iiic;itcil scales at the lines of 

 iiu'i'ciiiciil ; liiiii/c (■iir\iii^ ;i litllc ii|i\\;iri|, nitv iniif'li conlriU'ted and 

 .<h()i'l: siipcriar viilvr llal, wi'iiiklcil (■(Uicciil cicjillv. willuuil any a|i|icai"- 

 ance of loiiLiitiidiiial lines: liiin/c more dilalcil than that of the su|iiTior 

 valvt'. and ohli(|n(.' with r('S|icct to the t hiid<ii(',-> of the .-Indh'' Say, 

 1824. 



This is cue of the most abundant fossils in the Aquia formation. The 

 Nanjemoy formation contains many small oysters which are probably 

 the young of sellaeforniis, althoui;li they cannot he distingiiislied fi'iini 

 the young of this species. 



Length, 215 mm.; width, 180 mm. 



Occurrence. — Aquia Formation. Upper ]\Iarlboro, Hardesty, Aquia 

 Creek, Brooks Estate near Seat Pleasant, 3 miles west of Leeland on 

 Western Branch, SheckeFs Farm near South Eiver. Eeedy Run, Liver- 

 pool Point, 1^ miles south of Grimesville, Potomac Creek. Fort Wash- 

 ington, Tinkers Creek, 1 mile northeast of Piscataway, Swan Creek 

 (ravine near Piscataway Creek), 1 mile southeast of Mason Springs, 

 ]\Iouth of Paspotansa Creek, Wades Bay, 3 miles west of Pisgah, Clifton 

 Beach, Mattawoman Creek, 2 miles south of South Eiver, Glymont, 2 

 miles below Potomac Creek, Leeland, Seven River. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. Xational Museum, Philadelphia Academy of Xatural Sciences. 



OSTEEA COMPEESSIEOSTEA TAB. ALEPIDOTA Dall. 



Ost7-ea compressirostra var. alepidota Dall, 189S, Trans. W'aguer Free Inst. Sci., vol. 

 iii, part iv, p. 680. 



Description. — "'Without raised lamellae externally but with radial 

 o-rooves." Dall. 1898. 



