MARYLAND GEOLOGICAL SURVEY 625 



Shell very small and gibbous, between three and four millimeters in 

 altitude, the interior regularly ovate in outline; umbones inflated, 

 strongly prosogyrate and incurved, proximate ; external surface sculptured 

 with prominent and regularly spaced incrementals and resting stages; 

 radial sculpture microscopically fine, not over-riding the concentric ; liga- 

 ment lodged in a narrow groove running backward from beneath the 

 apices of the umbones ; inner margins strongly crenulate, the area directly 

 beneath the umbones slightly flattened and broadened and bearing four or 

 five pseudo-taxodont denticles; a more extended, but less clearly defined, 

 area developed in some individuals upon the medial portion of the pos- 

 terior lateral margin ; muscle scars and pallial lines indistinct. Crenella 

 serica Con. is a very abundant little bivalve in the Monmouth of Prince 

 George's County. 



Occurrence. MONMOUTH FORMATION. Brightseat, Brooks estate near 

 Seat Pleasant, Friendly, 1 mile west of Friendly, Prince George's County. 



Collections. Maryland Geological Survey, New Jersey Geological Sur- 

 vey, U. S. National Museum. 



Outside Distribution. Matawan Formation. Marshalltown clay marl. 

 New Jersey. Monmouth Formation. Eed Bank sand, New Jersey. 

 Peedee Sand. North and South Carolina. Ripley Formation. Exogyra 

 costata zone, Georgia ; Eufaula, Alabama. Selma Chalk. Exogyra costata 

 zone, Tombigbee Eiver, Sumter County, Alabama; east-central Missis- 

 sippi ; Alcorn, Union and Tippah counties, Mississippi. Extreme top of 

 zone, Pataula Creek, Georgia; Lowndes County, Mississippi. 



CRENELLA ELEGANTULA Meek and Hayden 

 Plate XXXVI, Fig. 19 



Crenella elegantula Meek and Hayden, 1862, Proc. Acad. Nat. Sci., Phila., 



for 1861, p. 441. 

 Crenella elegantula Meek, 1864, Check List Inv. Fossils, N. A., Cret. and 



Jur., p. 11. 

 Crenella elegantula Meek, 1876, Kept. U. S. Geol. Survey, Territories, vol. 



ix, p. 75, pi. xxviii, figs. 6a-6c. 

 Crenella elegantula Weller, 1907, Geol. Survey New Jersey, Pal., vol. iv, p. 



511, pi. Ivi, fig. 6. 



