EOCENE TEREBRATULA 
21 
ments and none of its contemporaneous form with it? The forms 
accompanying the Eocene Terebratula are without exception dis¬ 
tinctly Eocene in aspect; and none of the other forms of the Ran- 
cocas come over with it. It is doubtful whether the Rancocas 
formation was ever present west of the Chesapeake Bay or south 
of the Sassafras River in Maryland. In the deposits containing 
the Aquia fossils, the sediments are uniformly fine. Currents of 
water with velocities great enough to transport such massive forms 
as this Terebratula would have undoubtedly brought in large 
pebbles and the matrix would have been formed of a conglomer- 
tic nature rather than of fine uniform greensand. 
' Attempts to explain T. Marylandica as T. harlani derived me¬ 
chanically from the Cretacic sediments meet with unsurmountable 
difficulties and may be dismissed as extremely improbable. 
Only Charles Schuchert suggests that the Eocene Terebratula 
might be a new species. Bagg,^ in a short article published in the 
American Geologist, advocates the view that the Eocene form is 
mechanically derived from destroyed Rancocas beds. Doctor 
Schuchert bases his opinion that it is a new species upon the pres¬ 
ence of certain differential specific characters. Evidently he saw 
only a few specimens as he states that it is not advisable to draw 
conclusions from single specimens. In the present connection a 
large number of specimens of the true ‘New Jersey and Delaware 
Terebratula harlani were studied and compared with an abundance 
of the Maryland Eocene forms. 
The following is a description of the Maryland Eocene form: 
Test very large, the average of several large individuals being 77 mm. 
in length, 47 mm. in width, and 41 mm. in thickness. 
Shape: Edges subparallel, smooth and well coordinated. Adult speci¬ 
mens cylindrical in outline; bilobation absent in nearly all specimens and 
reduced to relative insignificance in those which possess it; young speci¬ 
mens are very unlike the adults in shape, presenting a triangular outline 
from above, and a slight thickness. 
Ventral Valve: Very convex, beak very pointed, very prominent and 
slightly curved; foramen 3 to 5 mm. in diameter; no appearance of any 
trough-like groove down the median portion of the valve; no trace of 
any angular ridge running downward from the apex as in T. harlani; 
truncation lines very fine and wavy, and become more and more parallel to 
the edge on approaching it, no sharp breaks in these lines as in T. harlani; 
edges of the valve uniformly straight; compared with the dorsal valve it 
3 American Geologist, Vol. XXIII, p. 370, 1898. 
