MARYLAND GP:OLOGICAL SURVEY 223 



be any other species at the St. Mary's River for which the description 

 could have been intended. Conrad described the form as follows : 



"Shell turreted, smooth, polished, longitudinally ribbed; whorls 

 slightly convex ; suture impressed ; aperture ovate. One-fifth of an inch 

 in length. It has some resemblance to the Turho simillimus of Montagu, 

 but the ribs are more numerous, and it is also a larger species." 



"Pasithea" exarata H. C. Lea is a TurboniUa which differs from this 

 in having elevated rounded ribs which are somewhat curved. It is prob- 

 ably a distinct species or at least a variety. If intermediate forms bridg- 

 ing the gap between nivea and exarata should be found. Lea's name 

 would of course have priority. The material now at hand does not justify 

 us in uniting the species. 



The Maryland forms are exactly like those from the Pliocene and 

 Pleistocene of the Carolinas Avhich Dr. Dall referred to Stimpson's 

 species, Init they do not agree very closely with Stimpson's description. 

 For example, instead of having the "raised longitudinal ribs" which 

 Stimpson describes, the Miocene specimens have impressed longitudinal 

 grooves with narrower interspaces. The grooves cease at the periphery 

 of the whorl but the general level of the interspaces is maintained beyond 

 on the base of the whorl. 



Length, 6 mm.; diameter, 1^- mm. 



Occurrence. — St. Mary's Formation. St. Mary's River. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 Wagner Free Institute of Science. 



Turbonilla (CiHEMNiTziA) NIVEA Stimpson var. 

 Plate LIV, Figs. 11, 12. 



Description. — Shell small, slender, varying in acuteness of spire; 

 whorls, seven to ten gently convex; spiral sculpture absent; body whorl 

 with about thirty irregular, sometimes obsolete longitudinal ribs which 

 die out near the periphery of the body whorl; base rounded, mouth 

 elongate. 



Length, 5 mm. ; diameter, 1 mm. 



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

 Langley's Bluff. Choptank Formation. Jones Wharf. 



