MAHVI.AM) (!i:()l.()()IC \ I. SIUVKY 185 



Dcscripiion. — " Ovatf, iirnl'diindlv \ ciil ricosc, with (-(jarsc, irrcj^aihir 

 C'oiuciit lie lines aiul t'lin-nws, nml obsolete, rallicr distiint, radii; suiii- 

 iiiit n|' iiiiiliii |ir(iiiiiiiciil." ('(iiirad, 18-12, 



'I'lic \crv Irauilf ^l"'!! "I lids species was t'oiiiid only i)ai-lially pi'e- 

 served in a few inslnnccs. all lioii.Lili n iiincroiis casts were ohtainrd from 

 llic ii)ilni'al('d lavfi-. Zone o, at Aijidn Ci'cck. 



Length, 75 mm.: hciulil, r..") nun. 



Ornirrrnre. — Aqulv I'Dk.matiun. Clirion Jkacli (upper indurated 

 bed), A(|nia Creek, Fort Washington, Piscataway (Conrad). 



CoUrcHnns. — ^laryland (icologieal Survey, Philadelphia Academy of 

 Natui'al Sciences, dolins Hopkins rnivei'sity, U. S. National '^^lls{■llnl. 



Order PRIONODESMACEA. 



Family MYTILIDAE. 

 Genus MODIOLUS Lnmarck. 



Modiolus alabamensis Aldrich. 

 Plate XLIII, Figs, i, 5, 5a. 



Jfodiola alabamensis Aldrich, 1895, Bull. Amer. Pal. No. 2, p. 16, ul. v, fig. 13. 

 JTodiola potomacensis Clark, 189r», Johns Hopkins Univ. Circ, vol. sv, p. 5. 

 Modiola poiomacensis Clark, 1896, Bull. Ill, U. S. Geol. Survey, p. 85, pi. xxxiv, 



figs. Iff-lf. ■ 



Modiolus (Brachydontes) poiomacensis Dall, 1898, Trans. Wagner Free Inst. Sci., vol. 

 iii, pt. iii, p. 796. 



Description. — " Shell strongly arcuate, surface with raised lines closely 

 set, becoming nearly obsolete on the beaks; a few lines of growth cross- 

 ing the striae; beak small, hinge margin slightly curved, ascending; very 

 small fissure on basal margin." Aldrich, 1895. 



Shell small, oblong, thin, tumid, anterior side somewhat contracted; 

 surface with fine costated striae nearly obsolete anteriorly and less- 

 strongly accentuated posteriorly than in the center, crossed occasionally 

 by irregular lines of growth; unibones in'ominent, curved. 



Length, 33 mm.; width, 15 mm. 



Occurrence. — JSTaxjemoy Foematiox. Popes Creek, Woodstock, 2^ 

 miles above Popes Creek. Aquia Foematiox. Liverpool Point, Clif- 



