163 SYSTEMATIC PALEONTOLOGY 



Few of the specimens obtained show any traces of the shell substance^ 

 and rarely inijDressions of the transverse striations of the tnhe wall. 



Occurrence. — Aquia Fokmation. AqiTia Creek, Upper Marlboro. 



Collection. — Johns Hopkins University. 



Family SAXICAVIDAE. 



Genus PANOPEA Menaid. 



Panopea elongata Conrad. 



Plate XXXI, Figs. 1-5. 



Panopaea elongata Conrad, 1835, Trans. Geol. Soc. Penn., vol. i, p. 339, pi. xiii, tig. \. 

 Panopaea elongata Conrad, 1846, Amer. Jour. Sci., ser. ii, voL i, p. 21.5, pi. i, fig. 2. 

 Panopaea elongata H. C. Lea, 1848, Proc. Acad. Nat. Sci. Phila., vol. iv, p. 103. 

 Glycymeris elongata Conrad, 1854, Proc. Acad. Nat. 8ci., Phila., vol. vii, p. 29. 

 Olycymeris elongata Conrad, 1865, Amer. Jour. Concb., vol. i, p. 2. 

 Glycymeris elongata Conrad, 1866, Smitb. Misc. Coll. (200), p. 8. 

 Panopaea elongata Clark, 1895, Jobns Hopkins Univ. Circ, vol. xv, p. 4. 

 Panopaea elongata Clark, Bull. 141, U. S. Geol. Survey, p. 75, pi. xix, figs, la-lc. 

 Panopea elongata Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, pt. iv, p. 838. 



Description. — " Shell oblong, produced, surface with distinct con- 

 centric irregular undulations; beaks distant from the anterior margin."' 

 Conrad, 1835. 



Since at most localities casts alone are found, the following important 

 character has thus been overlooked, viz., that the surface is covered with 

 closely-set, radiating lines of minute granules, which when worn show 

 as lines of punctae, or give the surface an irregularly honeycombed ap- 

 pearance. 



Length, 85 mm.; width, 43 mm. 



Occurrence. — Aquia Foemation. Fort Washington, Winchester,. 

 " Piscataway " (Conrad), Tinkers Creek 1 mile north of Piscatawa}^, 1 

 mile northeast of Piscataway, 1 mile southeast of Mason Springs, Har- 

 desty, P. E. cut near Seat Pleasant, Aquia Creek, Potomac Creek, Pas- 

 potansa Creek, 2 miles below Potomac Creek, Marshall Hall, Upper 

 Marlboro, Clifton Beach, Eolphs Landing, Glymout. 



Collections. — Johns Hopkins University, Maryland (Jeological Survey, 

 Philadelphia Academy of Natural Sciences, U. S. National Museum. 



