MARYLAND GEOLOGICAL SUKVEY 275 



• Pholas arcuata Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. .571. 

 Pholas arcuata Meek, 1864, Miocene Check List, Smith. Misc. ColL (183), p. 12. 

 Barnea (Scobina) arcuata Dall, 1898, Trans. Wagner Free Inst. Sci.," voL iii, pt. iv, 

 p. 816. 



Description. — " Shell oblong-ovate, with numerous ribs, elevated on 

 the posterior side, and concentric wrinkled striae, lamelliform on the 

 anterior side; ribs squamose; base arcuated." Conrad, 1841. 



This species differs from P. costata found so abundantly at Cornfield 

 Harbor by being smaller, by having a longer umbonal reflection, and 

 by being thicker and stronger. We have only a few broken valves. 



Occurrence. — St. Mary's Formation. St. Mary's Eiver. 



Collection. — Maryland Geological Survey. 



Genus MARTESIA Leach. 

 Section ASPIDOPHOLAS Fischer. 



Martesia ovalis (Say). 



Plate LXV, Figs. 4, .5, 6, 7, 8, 9. 



Pholas ovalis Say, 1830, Amer. Jour. Sci., vol. ii, p. 39. 



Martesia (?) ovalis Dall, 1898, Trans. Wagner Free Inst. Sci., voL iii, pt. iv, p. 820, 

 pL xxxvi, fig. 5. 



Description. — " Tube equal, entire and rounded at base, and gradu- 

 ally attenuated towards the anterior termination. Shell subovate, de- 

 hiscent; valves with crowded, acute, elevated, transverse lines, some- 

 what decussate with longitudinal slightly indented ones, a more con- 

 spicuous longitudinal indented line before the middle, posterior basal 

 margin smooth; within equal, the posterior basal margin distinguished 

 by a slight undulation." Say, 1820. 



Shell small, oval, elevated, thin, and fragile; a radial furrow extends 

 obliquelj' across the shell from the beak to a point on the ventral margin 

 slightly posterior to the middle, from this point a fine curved line ex- 

 tends diagonally forward and upward to the upper part of the anterior 

 margin, thus dividing the surface into three portions, the anterior one 

 being smooth, extremely thin and usually entirely broken off, the mid- 

 dle one being covered with fine, close, distinct, minutely crimped 

 lamellae running parallel to the curved line, bounding them anteriorly; 

 the posterior portion with only rather coarse, irregular, concentric 



