334 SYSTEMATIC PALEONTOLOGY 



Occurrence. — Calve'^t Foemation. Plum Point. 

 Collection. — Maryland Geological Survey. 



Aligena pustulosa Dall. 

 Plate LXXXIX, Figs. 5a, 5b. 



Aligena pustulosa Dall, 1898, Trans. Wagner Free Inst. Sci., vol. ill, jit. iv, p. 928, 



pi. xxxiii, tigs. IS, 22. 

 Aligena pustulosa Dall, 1900, Trans. Wagner Free Inst. Sci., vol. iii, pt. v, p. 1176. 



Description. — " Shell small, thin, subtrigonal, moderately inflated, 

 subequilateral, with small, pointed, inconspicuous beaks; valves with a 

 well-marked carina extending downward and forward to the anterior 

 angle of the basal margin, in front of which keel the surface is slightly 

 impressed; surface sculptured with feeble incremental lines, along which 

 are irregularly distributed, small, pointed, pustular elevations; beaks 

 anteriorly twisted with a minute obscure tooth below them on the 

 cardinal margin; ligamentary sulcus long and well marked; scars and 

 pallial line much as in Diplodonta; margin entire, inner surface faintly 

 radially striated. Alt. 6, lat. 5.2. diam. 4 mm." Dall, 1900. 



Occurrence. — Calvert Formation. " Calvert Cliffs " (= Plum 

 Point?). 



Collection. — U. S. National Museum. 



Superfamily LUCINACEA. 

 Family DIPLODONTID/E. 



Genus DIPLODONTA Brown. 



Diplodonta acclinis Conrad. 



Plate LXXXIX, Figs. 6a, 6b. 



Lucina acclinis Conrad, 1832, Fossil Shells of the Tertiary, p. 21, pi. vi, tig. 2. 

 Mysia americana Conrad, 1838, Fossils of the Medial Tertiary, p. 30, pi. xvi, fig. 2. 

 Diplodonta acclinis Conrad, 18.58, Proc. Acad. Nat. Sci. Phila., vol. ix, p. 166. 

 Mysia acclinis Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 577. 

 Mysia acclinis Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 8. 

 Diplodonta acclinis Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, pt. iv, pi. 



xxviii, figs. 2, 13. 

 Diplodonta acclinis Dall, 1900, Trans. Wagner Free Inst. Sci., vol. iii, pt. v, p. 1186. 



Description. — " Suborbicular, or lentiform, a little oblique, with strong 



lines of growth; hinge with 2 diverging teeth in each valve; posterior 



