\l\i;vr,.\XD OKOI.OfilOAL SURVEY 147 



Length, 35 mm.; wiclUi (of l)()(ly wlmil). H) nini.; IciiliIIi nl' posterior 

 digitation, 22 mm. 



Occurrence. — Aquia FoFnr\Trox. 1 mile noTthcnst of Piscataway, 

 PaspotiUisii Crook, 2 miles lidow I'dtdiiiac ('reck. 



Collcclioii. — ^Maryland (Joolonic'al Survey. 



Family TURRITHLLIDAE. 



Genus TURRITHLLA l.amarck. 



TuERiTELLA MoiiTOXi Courad. 



Plate XXVI, Figs. 1-5. 



TnrrHella mortoni Conrad, ISiJO, Jour. Acad. Nat. Sci. Pliila., vol. vi, p. 2;il, pi. x, 



tig. -i. 

 Tnrritella mortoni Courad, 18:J3, Fossil Shells of the Tertiary, No. 3 [2ud Edit.], 



p. 40, pi. XV, fig. 11. 

 Turritdla mortoni Morton, 1834, Synopsis Organ. Rem. Cretaceous Group, App., 



p. 4. 

 Tnrritella mortoni H. C. Lea, 1848, Proc. Acad. Nat. Sci. Phila., vol. iv, p. 107. 

 Turritella mortoni Conrad, 1865, Amer. Jour. Conch., vol. i, p. 32. 

 Turritella mortoni de Gregorio, 1890, Ann. Geol. et Pal., p. 132, pi. xi, fig. 7. 

 Tnrritella mortoni var. postmortoni Harris, 1894, Amer. Jour. Sci., ser. iii, vol. xlvii, 



p. 303, fiss. 1, 2, 3. 

 Turritella mortoni Clark, 1895, Johns Hopkins Univ. Circ, vol. xv, p. 4. 

 Turritella mortoni C\iiT:'k,\'&di3, Bull. 141, U. S. Geol. Survey, p. 69, pi. xiii, figs. 



la-le. 

 Turritella mortoni Harris, 1899, Bull. Amer. Pal., No. 11, p. 74, pi. x, figs. 3, 4. 



Descriftion. — " Shell tiirreted, conical, thick, with revolving distant, 

 and finer intervening striae; whorls with an elevated acute carina near 

 the base of each; volutions about eleven; the striae are largest on the 

 elevations of the whorls, which are slightly concave above, and abruptly 

 terminate at the sutures; the lines of growth on the last whorl are strong 

 and much undulated.'' Conrad, 1830. 



This important species was one of the first to be recognized in the 

 Maryland Eocene, and has been generally regarded as one of the most 

 characteristic, as it is one of the most common forms. At times it 

 makes up Avhole beds, as shown in the Paspotansa member of the Aquia 

 formation at Aquia Creek, Potomac Creek, and other neighboring lo- 

 calities. 



Turritella mortoni shows very great variations in the form and deco 



