400 SYSTEMATIC PALEONTOLOGY 



eons impressed; striated, the margins not pouting in the middle; beaks 

 prominent, obtuse; interior brilliantly pearly, muscular impressions deep; 

 the basal margins finely crenulate ; hinge strong, wide ; the chondrophore 

 oblique, heavy; anterior teeth wide, strong, about seventeen, posterior 

 about seven. , . . 



" This species differs from the preceding [N. cJiipolana] by its more 

 trigonal, heavy, and pearly shell, its wider and proportionately heavier 

 hinge, and its impressed instead of merely flattened escutcheon. The 

 Maryland specimens are usually larger and more worn than, the types 

 from West Florida; both retain a purplish tint in their nacre." Dall, 

 1898. 



Length, 4.75 mm.; height, 4 mm.; diameter, 2.5 mm. (Dall). 



Occurrence. — St. Mary's Formation. Cove Point, Langley's Bluff, 

 St. Mary's Eiver. Choptank Formation. Jones Wharf. 



Collections.— liaTyland Geological Survey, Johns Hopkins University, 

 U. S. National Museum. 



NucuLA taphria Dall. 

 Plate CVIII, Figs. 9, 10, 11. 



Nucula taphria Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, pt. iv, p. 576, 

 pi. xxxii, fig. 14. 



Description. — " Shell small, very solid, rounded cuneiform, with few 

 strong, distant concentric grooves, like marks of resting stages, which 

 extend clear over the shell, otherwise smooth; beaks prominent, turgid; 

 lunule absent; escutcheon faintly indicated; posterior end subtruncate, 

 anterior produced and rounded, base moderately arcuate; interior hardly 

 nacreous, muscular impressions large and distinct; basal margins entire; 

 hinge strong and heavy; chondrophore wide, distinct, a little oblique; 

 anterior teeth thirteen, posterior six or seven. . . . 



" This interesting species is related to the recent N. delphinodonta 

 Mighels, which is a more rounded and less oblique shell, without thip 

 strong concentric grooves of N. taphria." Dall, 1898. 



Length, 2.9 mm.; height, 2.25 mm.; diameter, 1.5 mm. (Dall). 



Occurrence. — St. Mary's Formation. St. Mary's Eiver. Choptank 

 Formation. Jones Wharf. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum. 



