236 SYSTEMATIC PALEONTOLOGY 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 TJ. S. National Museum, Philadelphia Academy of Natural Scisnces, 

 Wagner Free Institute of Science, Cornell University. 



TuRRiTELLA VARIABILIS Conrad. 

 Plate LVII, Fig. 1. 



Turritella variabilis Courad, 1830, Jour. Acad. Nat. Sci. Phila., vol. vi, 1st ser., 



p. 221, pi. X, tig. 3. 

 Turritella variabilis Conrad, 1842, Proc. Nat. lust., Bull, ii, p. 187. 

 Turritella variabilis Courad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 568. 

 Turritella variabilis Meek, 1861, Miocene Check List, Smith. Misc. Coll. (183), p. 16. 



Description. — " Shell subulate, turreted, tapering to an acute apex; 

 whorls flattened in the middle, with from two to five smooth ribs on each, 

 and transversely striated; suture impressed. 



" The ribs are generally three in number, but a variety occurs with . 

 two only, or the intermediate one becomes obsolete. The largest speci- 

 mens, which much exceed the figure in size, sometimes have five ribs on 

 each whorl.'" Conrad, 1830. 



This species is extremely variable and has been described under many 

 names. The varieties described below with the synonyms quoted under 

 each include all the names which have been applied to Maryland speci- 

 mens. These varieties can be clearly recognized in the adult specimens, 

 but the young cannot be separated. 



The name T. variahilis has been applied only to specimens from St. 

 Mary's Eiver and the typical form of the species is here regarded as re- 

 stricted to that horizon. It is distinguished by its moderately but uni- 

 formly convex whorls with many revolving ribs, from two to five of which 

 are larger than the rest, uniformly distrilmted over the whorl, and of 

 equal prominence. 



Length (restored), 80 mm.; diameter, 13 mm. 



Occurrence. — St. Mary's Formation. St. Mary's Eiver, Cove Point, 

 Langley's Bluff. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum. 



