M.\i(Vi.\M) (;i;(»i,(m;i(\i, srii\i:v 127 



liiif. W'IkuIs of (lie spire with foiir nodular rcvciU iii;^ lines hehnv the 

 siKMildcr. 



I.en*^t li, I •- mm.; w idtli. I mm. 



Occurrence. — Aqtia I'"()I(M a tion. 1 mile suntlica.-i (if .^^a^()n Springs. 



CoUcrlloit. — ^raryland ( leoldiiical Survey. 



Subgciuis IIHjMII'LHUKO'I'OMA Cossmaiin. 



Plkuhotoma (IIkmii'leurotoma) ciiildreni Lea. 

 Plate XX, Figs. 10, 11. 



Plenrotoma ciiildreni Lea, 1833, Contrib. to Geol., p. 187, pi. iv, litr. ]3:i. 

 Pleurotoma denticnla var Harris, 1899, Bull. Amer. Pal., No. 11, p. 12, pi. i, tigs. 

 21, 22. 



Description. — "Shell fiisifonn, tiirrited, transversely striate, granu- 

 late on the larger part of the whorl; substance of the shell rather thick; 

 sjiirc elevated, obtuse at apex; whorls about nine, subcanaliculate above; 

 mouth long and narrow, one-third the length of the shell." Lea, 1833. 



Our specimens vary considerably in the smaller details of sculpture, 

 but all seem to fall within the limits of variation of the Alabama form. 

 Whether they are the same as the French species P. denticnla Bast, to 

 which Professor Harris assigns the Alabama form is a question that 

 cannot be settled here. They agree witli it well enough to fall into the 

 subgenus Hemipleurotomn of which P. denticnla is the type. 



Length, 12 mm.; width, 3.5 mm. 



Occurrence. — Aquia Formatiox. 1 mile southeast of Mason Springs, 

 2 miles below Potomac Creek. 



Collection. — Maryland Geological Survey. 



Pleurotoma piscataa'exsis n. sp. 

 Plate XX, Fig. 12. 



Descriptio)t. — Shell fusiform, seven-whorled, carinated: lines of growth 

 distinct; revolving lines absent above the shoulder, one to three in num- 

 ber below the shoulder; beak marked only by lines of growth; nucleus 

 three-whorled, smooth; following whorls of tlje spire with oblique pli- 

 cae, extending from suture to suture; body whorl with about ten acute 

 nodes, confined to the suture. 



