238 SYSTEMATIC PALEONTOLOGY 



This variety includes all those forms from the Choptank and Calvert 

 formations which are characterized by the presence of two revolving ribs, 

 approximately equal in size and equally distant from the upper and 

 lower sutures of the whorls, with a somewhat smooth concave band be- 

 tween them. 



This variety represents an archaic condition retained longest in the 

 individuals from the Calvert formation, but almost always present on 

 the early whorls of individuals from the Choptank formation, and occa- 

 sionally seen on those from the St. Mary's formation. 



Length, 70 mm. ; diameter, 12 mm. 



Occurrence. — Choptank Formation. Greensboro, Dover Bridge, 

 Peach Blossom Creek, Flag Pond, Governor Run, 2 miles south of Gov- 

 ernor Run, Trappe Landing, Jones "\^Tiarf, Turner, Pawpaw Point. Cal- 

 vert Formation. Church Hill, Reed's, Plum Point, Chesapeake Beach, 

 3 miles south of Chesapeake Beach, Truman's Wharf. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. N'ational Museum. 



Turkitella variabilis var. exaltata Conrad. 

 Plate INll, Fig. 5. 



Tarritella exaltata Conrad, 1S41, Proc. Acad. Nat. Sci. Phila., vol. i, p. 33. 

 Turritella exaltata Conrad, 1842, Jour. Acad. Nat. Sci. Phila., vol. viii, 1st ser., p. 188. 

 Turritella exaltata Conrad, 18'42, Proc. Nat. Inst., Bull, ii, p. 182. 

 Turritella exaltata Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 567. 

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

 Turritella exaltata Harris, 1893, Amer. Jour. Sci., ser. iii, vol. xlv, pp. 24, 25. 



Description. — " Subulate, profoundly elongated ; whirls convex, with 

 spiral striae; base of each with a slight groove, and carinated line which 

 margins the suture; waved longitudinal rugse robust." Conrad, 1842. 



This variety includes all those forms in the Calvert formation which 

 have convex whorls with a revolving rib near the base. It differs from 

 var. alticostata in having a single revolving rib which is placed nearer 

 the suture than is the more prominent rib of that variety. 



Length, 140 mm. ; diameter, 14 mm. 



Occurrence. — Calvert Formation. Plum Point, Chesapeake Beach, 

 3 miles south of Chesapeake Beach. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. Xational Museum. 



