MARYLAND GEOLOGICAL SURVEY 317 



found incurvature of the beaks seem to have been perhaps the most promi- 

 nent characteristics in his mind — just as they produce the more striking 

 of the two forms — the name /. marlcoei will here be used to designate the 

 species with highly elevated, narrow, prolonged, profoundly incurved 

 beaks, a feature well represented in the right hand drawing of each of his 

 figures. It is about as high as long; posterior margin quite or almost 

 entirely arched ; dorsal slope crossed by two or three broad, deep, concen- 

 tric undulations marking resting stages during growth. 



licngth, 48 mm. ; height, 46 mm. ; diameter, 27 mm. 



Occurrence. — Calvert Formation. Plum Point (rare). 



Collection. — Maryland Geological Survey. 



Tsocardia mazlea n. sp. 

 Plate LXXXIV, Figs. 4, 5. 



Isocarclia Markoei Conrad, 1842, Proc. Nat. Inst., Bull, li, p. 193, pi. ii, fig. 1 (left 



hand drawing only and diagnosis in part). 

 Isocarclia Markoei Conrad, 1845, Fossils of the Medial Tertiary, p. 70, pi. xl, fig. 3 



(left hand drawing only and diagnosis in part). 



Description. — Shell rounded, inflated; length greater than height: 

 umbo elevated, broad, short, only moderately incurved, not strongly pro- 

 jecting; dorsal slope crossed by several shallow and at times indistinct con- 

 centric undulations; posterior margin curved above, straight below and 

 meeting the base at an obtuse angle to which there extends a flattened 

 ridge which is bordered on the posterior slope by a broad, gently depressed 

 or grooved area. See also remarks under I. marl-oei. 



Length, 52 mm. ; height, 46 mm. ; diameter, 27 mm. 



Occurrence.— Calyeut Formation. Plum Point (rare). 



Collection. — Maryland Geological Survey. 



IsocARDiA riLiTERNA Say. 

 Plate LXXXV, Figs. 3, 4. 



Isocardia fraterna Say, 1824, Jour. Acad. Nat. Sci. Pliila., vol. iv, 1st ser., p. 143, 



pi. xi, fig. 1 a and b. 

 Isocardia rustica Conrad, 1838, Fossils of the Medial Tertiary, p. 20, pi. xi, fig. 1. 

 Isocardia Co7iradi d'Orbigny, 1853, Prod. Pal. Strat., vol. iii, p. 121. 

 Olossus rusticm Conrad, 1854, Proc. Acad. Nat. Sci. Phila., vol. vii, p. 29. 

 Biicardia fraUrnn Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 576. 

 Glossies fraterna Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 8. 

 Isocardia fraterna Dall, 1900, Trans. Wagner Free Inst. Sci., vol. iii, pt. v, p. 1066. 



