338 SYSTEMATIC PALEONTOLOGY 



Lncina trisulcata Tuomey and Holmes, 1856, Pleiocene Fossils of South Carolina, 



p. 63, pi. xviii, figs. 18, 19. 

 Lucina trisulcata Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. .577. 

 Lncina trisulcata Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 8. 

 Lucina trisulcata Whitfield, 1894, Mon. xxiv, U. S. Geol. Survey, p. 64, pi. x, figs. 



1-4. 

 Lncina crenulata Whitfield, 1894, Mon. xxiv, U. S. Geol. Survey, p. 63, pi. x, figs. 



7-15 (not of Conrad). 

 Fhacoides (Gavilucina) trisulcatus Dall, 1903, Trans. Wagner Free Inst. Sci., vol. iii, 



pt. vi, p. 1369. 



Description. — " Obovate, convex; with conceiitric lines, and two or 

 three distinct concentric furrows; lunule profound. Differs from L. 

 alveata of the lower tertiary in being less ventricose, and in the much 

 more profoundly impressed lunule; the cardinal teeth are also very 

 different." Conrad, 1841. 



Shell inequilateral, being somewhat produced anteriorly; beak, conse- 

 quently not medial; moderately convex or more usually rather flattened, 

 especially anteriorly; a small, flattened groove or depressed band ex- 

 tending from the beak backward along the posterior submargin; the 

 two or three concentric furrows very distinct or, again, very indistinct 

 or entirely wanting; or at times only one furrow present, being either 

 distinct or indistinct; margin crenulated. 



Specimens that are rather elevated and ornamented by fine concentric 

 ridges only approach rather closely to the form of P. 0)-enulatum, but 

 may be distinguished from it by having a heavier hinge area and a more 

 profound lunule and by being somewhat produced anteriorly and not 

 quite so elevated. Wliitfield has figured as P. crenulatum the smoother 

 form of P. trisulcatum from New Jersey. 



Length of large specimen, 8 mm.; height, 8.5 mm.; diameter, 2 mm. 



Occurrence. — Choptank Fokmation. Greensboro, Cordova. Cal- 

 VEET Formation. Chesapeake Beach, 3 miles south of Chesapeake 

 Beach, Plum Point, Truman's Wharf, 3 miles west of Centerville, Church 

 Hill. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum. 



