724 SYSTEMATIC PALEONTOLOGY 



Dimensions. Altitude 26 mm., latitude 49 mm. ; semi-diameter 

 8 mm. 



Panope bonaspes is smaller than either of the other Panopece repre- 

 sented within the area under discussion and differs from them both in 

 the smoothly rounded rather than obliquely truncate posterior margin. 



The species is perhaps the most conspicuous member of the M ago thy 

 bivalve fauna. 



Occurrence. MAGOTHY FORMATION. Good Hope Hill, District of 

 Columbia. 



Collection. Maryland Geological Survey. 



Superfamily ADESMACEA 

 Family PHOLADIDAE 



Genus PHOLAS Linne 

 [Systema naturae, ed. x, 1758, p. 669] 



Type. Pliolas dactylus Linne. 



Shell thin, brittle, often strengthened externally by accessory plates, 

 elongate, cylindrical, gaping anteriorly; valves reflected at the umbones, 

 the space beneath divided by radial septa into cellular chambers; hinge 

 plate furnished with myophorial process; sculpture not uniform over the 

 surface of the valve; pallial sinus long and deep as would be inferred 

 from the long siphons which are united excepting at the ciliated 

 extremities. 



The genus has been in existence since the Jurassic. It is represented 

 to-day by about twenty species, all of them burrowers in clay, wood or 

 even rock, and all possessing the property of phosphorescence. 



PHOLAS PECTOROSA Conrad 

 Plate XLV, Fig. 1 



? t Pholas cithara Morton, 1834, Syn. Org. Rem. Cret. Group, U. S., p. 68, 



pi. ix, fig. 10. 

 Pholas pectorosa Conrad, 1854, Proc. Acad. Nat. Sci., Phila. for 1852-53, p. 



200. 



Etymology: 0wXdy, lurking in a hole. 



