276 SYSTEMATIC PALEONTOLOGY 



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

 and curved posteriorly: within, chondrophore 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 laterally 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. rliomljoidea H. C. Lea is, as remarked by him in describ- 

 ing it, not just identical with M. ovaliSj aJ though the differences 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. Maey's Foemation. Cove Point, St. Mary's Eiver. 

 Choptank Foematiox. Jones Wharf, Pawpaw Point, St. Leonard 

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

 Plum Point, White's Landing, Reeds. 



Collections. — ]\raryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum. 



Superfamily MYACEA. 

 Family SAXICAVID/E. 



Genus PANOPEA Menard. 



Paxopea whitfieldi Ball. 

 Plate LXV, Fig. 10. 



Panopcea Goldfussii Whitfield, 1894, Mon. xsiv, U. S. Geol. Survey, p. 89, pi. xvi, 



figs. 9-13. 

 Not Panopea Goldfussii Wagner, 1838. 

 Panopea \\Mtfleldi 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- 



