194 SYSTEMATIC PALEONTOLOGY 



Collections.— llaryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum. 



NaSSA GREENSBOROi^NSIS U. Sp. 



Plate XLIX, Figs. 5a, ob. 



Description. — Shell small, narrow, elongate, six-whorlecl ; whorls con- 

 vex, separated by very distinct sutures; sculptured by faint longitudinal 

 undulations which are overridden by about ten fine spiral striae on each 

 whorl; strias separated by interspaces of the same width as the stria; 

 aperture l^roadly ovate ; outer lip with four beads. 



Length, 7 mm.; diameter, 3.3 mm. 



Occurrence. — Choptank Formation'. Greensboro. 



Collection. — Maryland Geological Survey. 



ISTassa marylandica n. sp. 



Plate XLIX, Figs. 6, 7, 8. 



Description. — Shell small, solid, elongate (except as noted below), 

 eight-whorled ; body whorl with 9 to 15 distant raised longitudinal ribs 

 which extend to the suture without any constriction or subsutural tuber- 

 cles, and with 25 to 30 faint revolving lines of uniform strength which 

 never override the ribs; whorls of the spire with about 10 revolving lines. 



This species differs from N. peralta, with which it is associated, in 

 being generally smaller (and more elongated), in having a less distinct 

 suture, in having constantly fewer and more distant ribs which are never 

 overridden by the revolving lines and which extend from suture to suture 

 without constriction. 



Associated with this species are two forms which further study may 

 show to be entitled to separate names, but at present it seems best to 

 include them here as aberrant forms of this species. One is very short 

 and globose (fig. 8), while the other has a distinct notch near the lower 

 end of the labrum (fig. 7). Otherwise they have all the characteristics 

 of this species. 



Length, 14 mm. ; diameter, 6 mm. 



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



Collections. — J\laryland Geological Survey, Johns Hopkins University^ 

 Wagner Free Institute of Science. 



