Maryland Geological Survey 523 



moderately curved, more prominent just in advance of the beaks. Surface 

 of the shell polished or marked by very fine concentric lines of growth, 

 except on the posterior cardinal slope, where they unite and form a few 

 inconspicuous folds. The interior of the shell shows the hinge-line to be 

 marked by several small transverse teeth on the anterior side, and on the 

 posterior side they extend almost to the hinge extremity." — Whitfield, 

 1885. 



P. protexta is represented in Maryland only by incomplete individuals 

 which contribute nothing to the knowledge of the characters of the species. 



Occurrence. — Monmouth Formation. Brooks estate near Seat Pleas- 

 ant, Prince George's County. 



Collections. — Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences, U. S. National Museum. 



Outside Distribution. — Matawan Formation. Merchantville clay marl, 

 Woodbury clay and Wenonah sand, New Jersey. Monmouth Formation. 

 Tinton beds, New Jersey. Eutaw Formation (Tombigbee sand). Exo- 

 gyra ponderosa zone, Mortoniceras subzone of Georgia. Eipley Forma- 

 tion. Exogyra costata zone, Houston, Mississippi; extreme top of zone, 

 Georgia. Selma Formation. Exogyra costata zone, east-central Mis- 

 sissippi. 



Perissonata littlii n. sp. 

 Plate XX, Figs. 1, 2 

 Description. — Shell compressed almost to a single plane, transversely 

 elliptical in outline ; umbones within the anterior fourth, indicated merely 

 by the focusing of the faint concentric striations, scarcely breaking the 

 contour of the dorsal margin and the faint lateral curvature ; anterior and 

 posterior dorsal margins converging at an angle of 165° or 170° ; posterior 

 dorsal margin broadly and gently constricted behind the umbones, 

 approximately horizontal in general direction; anterior dorsal margin 

 sloping away from the horizontal at an angle of not far from 5° ; anterior 

 lateral margin rounding broadly and smoothly into the base line; 

 posterior lateral margin broken, but the growth lines indicate an obscure 

 truncation ; base line broadly arcuate, merging much more gradually into 



