578 Systematic Paleontology 



Clay and Alcorn counties, Mississippi. Pierre Shales. Western Interior. 

 Senonian. Mexico, England, France, Germany, Bohemia, Switzerland, 

 Spain, Portugal, Belgium, Russia, Poland, Egypt, Algiers, Syria. Aria- 

 loor Formation. Southern India. 



Geyphjsa (Pycnodonte) pusilla n. sp. 

 Plate XXXIII, Pigs. 4-6 



Description. — Shell small, solid, dwarfish in general aspect, inequi- 

 valve, slightly inequilateral ; left valve moderately convex, the maximum 

 convexity at the medial portion of the shell ; right valve flattened or even 

 inclined to be concave ; umbone in the left valve anterior, evenly inflated, 

 orthogyrate, anterior end of left valve evenly rounded, posterior end pro- 

 duced somewhat obliquely ; ventral margin asymmetrically arcuate ; right 

 valve more regularly ovate in outline, the dorsal and the lateral margins 

 obscurely truncate, the base line strongly arcuate; external surface 

 smooth excepting for incremental sculpture which is most pronounced 

 toward the ventral margins of the right valve and along the dorsal mar- 

 gins of the left ; ligament area narrow, trigonal, the ligament groove only 

 slightly impressed; submargins of both right and left valves sculptured 

 with prominent crowded vermicular corrugations ; the single adductor 

 muscle scar conspicuous, above and slightly behind the median line ; pallial 

 scar distant from the ventral margin. 



Dimensions. — Left valve, altitude 34 mm., latitude 37 mm., semi- 

 diameter 13.6 mm.; right valve, altitude 39.5 mm., latitude 40.5 mm., 

 semi-diameter 7.6 mm. 



This form is remarkable for its small size and solidity, and for the 

 prominence of the vermicular sculpture of the submargins. It may 

 possibly prove to be a dwarfish type of P. vesicularis Lam., but nothing 

 quite like it occurs in any of the abundant and varied material that 

 represents the group in Maryland. 



Occurrence. — Monmouth Formation. Bohemia Mills, Cecil County. 



Collection. — Maryland Geological Survey. 





