'v86 SYSTEMATIC PALEONTOLOGY 



Family MACTRID/E. 

 Subfamily MACTRIN/E 



Genus MACTRA (L ) Lamarck. 



Mactra clathrodon Lea. 

 Plate LXIX, Figs. 1, 8, 9. 



Mactra clathrodon Lea, 1833, Contrib. to Geology, p. 212, pL vi, lig. 233. 



Mactra subcuneata Conrad, 1838, Fossils of the Medial Tertiary, p. 38, pi. sv, tig. 3. 



Mactra clathrodon Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, pt. iv, p. 893. 



Description. — " Shell subtri angular, thin, inequilateral, obscurely and 

 transversely striate; beaks somewhat pointed; lateral teeth crossed by 

 equidistant minute strise; excavation of the pallial impression small and 

 rounded; anterior and posterior cicatrices scarcely visible; cavity of the 

 shell somewhat deep; cavity of the beaks rather deep." Lea, 1833. 



Lea's type specimens are the young of the same species whose adult form 

 Conrad later described as M. subcuneata. 



Length, 33 mm. ; height, 25 mm. ; diameter, 7 mm. 



Occurrence. — St. Mary's Formation. Cove Point, Langley's Bluff, 

 St. Mary's Eiver. Calvert For:\iation. Plum Point, 3 miles west of 

 Centerville. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



Genus SPISULA Gray. 



Subgenus HEMIMACTRA Swainson. 



Section MACTROMERIS Conrad. 



Spisula (Hemimactra) delumbis (Conrad). 



Plate LXIX, Fig. 10. 



Mactra delumbis Conrad, 1883, Fossil Shells of the Tertiary, p. 36, pi. xi. 

 31actra delumbis Conrad, 1838, Fossils of the Medial Tertiary, p. 37, pi. xv, tig. 1. 

 Mactra delumbis Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 572. 

 Mactra delumbis Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 11. 

 Mactra Virginiaua Conrad, 1867, Amer. Jour. Conch., vol. iii, pp. 188, 369, pi. xxii, 



fig. 4. 

 Mactra [Schisodesma) delumbis Whitfield, 1894, Mon. xxiv, U. S. Geol. Survey, p. 82, 



pi. XV, fig. 10. 

 Spisula {Hemimactra) delumbis Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, 



pt. iv, p. 897, pi. xxvii, fig. 36. 



