140 SYSTEMATIC PALEONTOLOGY 



The occurrence and further description is given below under each 

 variety. 



Terebra (Acus) curvilineata var. whitfieldi n. var. 

 Plate XL, Figs. 3, 4. 



Terehra curvilineata Whitfield, 1894, Mon. xxiv, U. S. GeoL Survej', pi. xx, figs. 

 15-17. 



Description. — Shell elongated, tapering slowly; whorls with a slight 

 constriction below the suture (in the mature individuals) above which 

 the longitudinal ribs arc very slightly tuberculate. In the young shells 

 the longitudinal ribs are continuous, without interruption or undulation, 

 from suture to future. Between the ribs are fine but sharp revolving 

 striae. 



The young of this variety bears a very strong resemblance to Terebra 

 (Hastula) venvsta Lea, of the Claibornian Eocene, and probably vennsta 

 is the ancestral form. The resemblance is so close that if the characters 

 did not change so much in the adult we would have to refer some of our 

 young specimens to the Eocene species. 



This variety occurs in the Calvert Formation at Jericho, N. J., and 

 is represented by figures 15 to 17 of Whitfield's report. 



Length (of fragment), 16 mm.; diameter, 5.7 mm. 



Occurrence. — Calvert Formation. Plum Point. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



Terebra (Acus) curvilineata var. dalli n. var. 

 Plate XL, Fig. 5. 



Terebra simplex, small var. Harris, 1893, Amer. Jour. Sci., ser. iii, vol. xlv, p. 24. 

 Terebra [Acus) curvilineata Dall, 1895, Proc. U. S. Nat. Museum, vol. xviii. [No. 

 10351, p. 36. (In part.) 



Description. — Shell acute; whorls flat-sided or very slightly convex; 

 ribs becoming obsolete on the later whorls, usually continuous — never 

 entirely cut by a subsutural band; a slight subsutural constriction is 

 sometimes present, but it produces merely a slight undulation in the 

 ribs; revolving lines extremely faint or entirely absent. 



This variety includes all those forms referred by Dall to curvilineata 



