INSTITUTE OF SCIENCE, PHILADELPHIA. 91 



the sinual inflection. In Say's P. rcflexa, as well as in the Florida fossil and 

 P. Menardi, the hinge-line is about equally elevated both anteriorly and 

 posteriorly, the beaks are somewhat anterior, and the sinual inflexion 

 relatively shorter and broader. The shell is also more massive. In view 

 of the differences here indicated, I would propose for the common form 

 of the Atlantic Middle Tertiaries, hitherto referred to Panopaa reflexa, 

 the name of P. cymbula, the species to be defined as follows : 



Panopsea cymbula, nov. sp. Fig. 20. 



Panop&a rcflexa, of most authors. 



Shell expanding anteriorly, where it is highest, gracefully rounded ; 

 rapidly sloping posteriorly, with the border reflected, permitting of a 

 broad gape ; beaks somewhat posterior, or beyond the middle, considera- 

 bly sloping, the apex directed slightly to the rear ; a prominent trans- 

 verse cardinal tooth beneath the apex, followed by a strortgly-bordered 

 cartilage plate ; muscular and pallial impressions rugged, deep ; sinual 

 inflection generally narrow and acutely pointed; external surface of 

 shell strongly and roughly furrowed. 



Length, 5.3 inches ; height, three inches. 



Miocene of the Atlantic slope. 

 Panopaea Floridana, nov. sp. Fig. 21. 



Shell oblique, expanding and ascending anteriorly, abruptly truncated 

 behind ; hinge-line in front of the umbones rising considerably, declivous 

 beyond the cartilage-plate, and ascending again toward the posterior 

 extremity ; posterior margin reflected, the shell gaping broadly ; umbones 

 well in front of the middle ; cartilage-plate very strong ; ligamental sulcus 

 deep ; muscular and pallial impressions well impressed, rough, the sinual 

 inflection often v-shaped. 



Length, 5.1 inches; height, three inches. 



Both valves of a single individual. 



This species can be readily distinguished from P. Menardi (P. reflcxa, 

 Say) by its truncated form, and the rise in the hinge-line in front of the 

 umbones ; the height of the gape is also relatively greater. 



Panopsea navicula, nov. sp. Fig. 22. 



Shell (known only by the right valve) short, broadly-oval, obliquely 

 rounded anteriorly, abruptly truncate behind, the gape (posterior) very 

 broad ; umbo in advance of the middle of the shell, the apex directed 

 forward ; hinge-line sigmoidal, or flexuously curved, ascending in front, 

 reflected posteriorly ; cardinal tooth prominent, arched upward ; cartilage 

 plate strong ; muscular and pallial impressions very deep, the sinual 

 inflection short and openly quadrangular; surface of shell prominently 

 sulcated. 



Length, five inches ; height, 3.5 inches. 



