566 Systematic Paleontology 



Point, Chesapeake and Delaware Canal. Delaware; head of Bohemia 

 Creek and Bohemia Mills, Cecil County; Brightseat, railroad cut 1 mile 

 west of Seat Pleasant, Brooks estate near Seat Pleasant, 1 mile west of 

 Friendly, Prince George's County, Maryland. 



Collections. — Maryland Geological Survey, New Jersey Geological Sur- 

 vey, U. S. National Museum, Geological Survey of India. 



Outside Distribution. — Monmouth Formation. Navesink marl, Red 

 Bank sand, and Tinton beds, New Jersey. In the eastern Gulf region 

 the species is generally distributed through the zone of Exogyra costata, 

 which includes the Bipley formation (typical marine beds) of northern 

 Mississippi, approximately the upper one-half or two-thirds of the Ripley 

 formation (typical marine beds) of eastern Alabama and Georgia. In the 

 Carolinas the species occurs throughout the Peedee sand. In Arkansas the 

 species ranges through the Malbrook marl, the Xacatoch sand, and the 

 Arkadelphia clay. In Texas the species is a common fossil in the Navarro 

 formation and its equivalent the " Webberville " formation. In Mexico 

 the species occurs in the Cardenas division of the so-called lower Senonian. 

 Ootatoor Formation. Southern India. 



Exogyea costata var. cancellata Stephenson 



Plate XXVII, Pig. 3 



Exogyra costata var. cancellata Stephenson, 1914, Prof. Paper, U. S. Geol. 

 Survey, No. 81, p. 53, pi. xx, figs. 2-4; pi. xxi, figs. 1, 2. 



Description. — " Shell of adult moderately thick ; subcircular to subovate 

 in outline; dimensions of an average specimen, length 92 mm., height 

 89 mm., convexity 41 mm. ; dimensions of a rather large specimen, length 

 117 mm., height 123 mm., convexity 58 mm. Left or lower valve much 

 larger than right valve and strongly convex ; attached in proximity of beak 

 to an external object, the beak usually somewhat deformed by the scar of 

 attachment; general form, hinge characters, and other internal shell 

 characters essentially the same as in Exogyra costata Say ; surface of shell 

 ornamented with more or less distinct, low, bifurcating, nodular costas, 

 the nodes produced by concentric depressions regularly arranged in such 



