276 SYSTEMATIC PALEONTOLOGY 



growth lines : imibonal reflection small, heavy, standing almost vertically 

 and curved posteriorly : within, chondrojjhore long, curved, narrow ; 

 posterior ligament area distinct, elongated, oval; median furrow showing 

 as a slight ridge : umbonal area covered by a large, elongated oval or 

 hour-glass shaped protoplax extending forward to below the middle of 

 the anterior margin, backward nearly to the ends of the valves and 

 covering a third of the side of the shell, being sometimes latei-ally con- 

 tracted into a somewhat hour-glass outline : shell enclosed in a calcareous 

 tube or siphonoplax lining the burrow, thin anteriorly, thickened and 

 contracted posteriorly : other accessory plates absent. 



This interesting little shell is found often riddling the valves of 

 Melina maxillata. There can be no doubt of its identity with Say's 

 species. M. rhomboidea H. C. Lea is, as remarked by him in describ- 

 ing it, not just identical with M. ovalis, although the difEerences are 

 slight and may not be of specific value, — still it is thought best not to 

 unite them without examining a series of specimens of Lea's species. 



Length, 16 mm.; height, 10 mm.; diameter, 5.5 mm. 



Occurrence. — St. Mary's Formation. Cove Point, St. Mary's River. 

 Choptank Formation. Jones Wharf, PaAvpaw Point, St. Leonard 

 Creek, Governor Run (lower bed), Cordova. Calvert Formation. 

 Plum Point, White's Landing, Reeds. 



Collections. — IMaryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum. 



Superfamiiy MYACEA. 

 Family SAXICAVID/E. 



Genus PANOPEA Menard. 

 Panopea whitfieldi Ball. 



Plate LXV, Fig. 10. 



Panopcea GoldfussU Whitfleld, 1894, Mon. xxiv, U. S. Geo). Survey, p. 89, pL xvi, 



ligo. 9-13. 

 Not Panopea GoldfussU Wagner, 1838. 

 Panopea Vihitfiddi Dall, 1898, Trans. Wagner Free Inst. Sci., voL iii, pt. iv, p. 839. 



Description. — Shell elongate-ovate; beaks approximate, not promi- 

 nent; anterior and posterior portions of the valves almost equal: ante- 



