330 SYSTEMATIC PALEOKTOLOGY 



Genus BORKMA Philippi. 

 BoKNiA MACTEOIDES (Coiirad), 

 Plate LXXXVITI, Figs. 6, 7, 8. 



Lepton mactroides Conrad, 1834, Jour. Acad. Nat. Sci. Phila. vol. vii, 1st ser., p. 131. 

 Lepton mactroides Conrad, 1838, Fossils of the Medial Tertiary, p. 19, pi. x, tig. fi. 

 Lepton mactroides Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 577. 

 Lepton mactroides M-QQ'k, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 8. 

 Bornia mactroides Dall, 1900, Trans. Wagner Free Inst. Sci., vol. iii, pt. v, p. 11.50. 



Description. — " Shell triangular, subequilateral, thin, convex, smooth 

 and polished; beaks prominent; central; basal margin straight; posterior 

 extremity less obtusely rounded than the anterior. Length less than 

 half an inch." Conrad, 1834. 



Length, 10 mm.; height, 7.2 mm.; diameter, 2 mm. 



Occurrence. — Choptank Formation. Governor Eun, 2 miles south 

 of Governor Eun, Jones ^yharf, Peach Blossom Creek, Dover Bridge. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



Bornia Triangula Dall. 

 Plate LXXXVIII, Figs. 9a, 9b. 



Kellia triangula H. C. Lea, MS., in Coll. Acad. Nat. Sci. Phila. 



Bornia triangula n. sp. ? Dall, 1900, Trans. Wagner Free Inst. Sci., vol. iii, pt. v, 

 p. 11.51. 



Description.— ^heW compact, elevated, triangular; anterior and pos- 

 terior dorsal margins declining at an obtuse angle from the beak; beak 

 distinctly prosocoelous and situated anterior to the middle of the shell; 

 anterior and posterior margins rounded; shell inflated just beneath the 

 beaks but mesially compressed near the basal margin; teeth distinct, shell 

 thin, polished; faint growth lines visible. 



Length, 5 mm.; height, 4.45 mm. 



Occurrence. — Calvert Formation. 3 miles west of Centerville. 



Collection. — Maryland Geological Survey. 



Bornia marylandica n. sp. 



Plate LXXXVIII, Fig. 10. 



Description. — Shell triangular depressed; inflated dorsally; gently 

 compressed mesially near basal margin; beak low, very markedly proso- 



