MARYLAND GEOLOGICAL SURVEY 235 



Turriiella plebeia Conrad, 1843, Proc. Nat. Inst., BulL ii, pp. 182, 187. 

 Turrilella pleheia Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 568. 

 Tiirritella octonaria Conrad, 1863, Proc. Acad. Nat. ScL Phila., vol. xiv, p. 568. 

 Tiirritella plebeia Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 16. 

 Turritella octonaria Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 16. 

 Turritella plebeia Harris, 1893, Amer. Jour. Sci., ser. iii, vol. xiv, pp. 25, 26, 27, 28. 

 Turritella {Mesalia ?) plebeia Whitfield, 1894, Mon. xxiv, U. S. Geol. Survej', p. 130, 

 pi. xxiii, tigs. 6-8. 



Description. — " Whorls convex, hardly flattened in the middle, with 

 about twelve revolving elevated striae, the middle ones alternately some- 

 what smaller; transverse wrinkles distinct." Say, 1824. 



The forms which have been referred to pleheia are considerably varied 

 in cliaracter and Say's description will not apply to them all. The 

 name is here used in a broad sense to cover all those Turritellas from 

 these beds whose whorls are more or less convex; are covered with fine, 

 uniform or uniformly alternating, raised, revolving striae; and are not 

 carinated. The typical form with very convex whorls, not flattened, 

 occurs throughout the Miocene, but is the only form in the St. Mary's 

 formation. A form (var. A) with almost flat whorls and an indistinct 

 suture occurs in the.Choptank and Calvert formations. The striae are 

 very uniform and closely set. At Plum Point the most abundant form 

 (var. B) has deep sutures and flat-topped whorls. It is smaller than 

 the typical form. 



The variety which Conrad described as Turritella octonaria is charac- 

 terized by having about eight prominent irregular revolving ribs with 

 intermediate ones. It occurs only in the Choptank formation at Dover 

 Bridge. 



Length, 47 mm.; diameter, 13 mm. {Typical form). 



Length, 22 mm.; diameter, 7 mm. {var. A). 



Length, 35 mm.; diameter, 10 mm. {var. B). 



Length, — mm.; diameter, 13 mm. {var. octonaria). 



Occurrence. — St. Mary's Pormation. St. Mary's River, Cove Point, 

 Langley's Blufl". Choptank Formation. Greensboro, Cordova, Peach 

 Blossom Creek, Dover Bridge, Flag Pond, Governor Eun (upper and 

 lower beds), 2 miles south of Governor Run, Jones Wharf, Pawpaw Point, 

 Calvert Formation. Plum Point, CJiesapeake Beach, 3 miles south of 

 Chesapeake Beach, Truman's Wharf. 



