648 SYSTEMATIC PALEONTOLOGY 



impressions large and strong, of abdut equal size ; pallia! line parallel with 

 the truncated posterior margin for a short distance below the posterior 

 muscular impression, then bending abruptly forward and continuing sub- 

 parallel with the shell margin." Weller, 1907. 



CrassatelUna carolinensis Conrad is represented in Maryland and Dela- 

 ware by a single imperfect cast. The species is apparently one of the most 

 reliable guide fossils of the Exogyra ponderosa zone. 



Occurrence. MATAWAN FORMATION. Post 105, Chesapeake and Dela- 

 ware Canal, Delaware. 



Collections. Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences, New Jersey Geological Survey, U. S. National Museum. 



Outside Distribution. Matawan Formation. Marshalltown clay marl, 

 New Jersey. Black Creek Formation. North and South Carolina. 

 Pcedee Formation. North and South Carolina. Eutaw Formation. 

 Basal. Exogyra ponderosa zone, Eussell County, Alabama. (Tombigbee 

 sand member). Mortoniceras subzone, Georgia; Eussell County, Ala- 

 bama; Prentiss County, Mississippi. Eipley Formation. Exogyra pon- 

 derosa zone, Barbour County, Alabama. Exogyra costata zone, Union 

 County, Mississippi. Extreme top of zone, Pataula Creek, Georgia. Selma 

 Formation. Exogyra costata zone, east-central Mississippi. 



Genus CRASSATELL1TES Kriiger 

 [Arch. Neuest. Entd. Urwelt, vol. ii, 1828, 4661 



Type. Crassatella gibbosula Lamarck. 



" Shell solid, inequilateral, slightly inequivalve, usually subtrigonal, 

 the posterior end longer ; valves closed, the ligament and resilium adjacent 

 and internal ; hinge of three cardinals in the right valve, of which the pos- 

 terior is more or less effaced by the resilium, and two in the left valve ; the 

 anterior edge of the right and the posterior edge of the left hinge margin 

 grooved to receive the edge of the opposite valve, which is bevelled to 

 serve as a lateral lamina ; sculpture chiefly concentric and often obsolete 

 except near the umbones." Dall, 1903. 1 



Etymology: Crassus, thick, heavy. 



1 Trans. Wagner Free Inst. Sci., Phila., vol. iii, pt. vi, pp. 1466, 1467. 



