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 J. marhoei 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 imdulations marking resting stages during growth. 



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



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



Collection.— M.axy\2.n^ Geological Survey. 



Tsocardi.a mazlea n. sp. 

 Plate LXXXIV, Figs. 4, 5. 



Jsocardia Markoei Conrad, 1842, Proc. Nat. Inst., Bull, ii, p. 193, pi. ii, flg. 1 (left 



hand drawing only and diagnosis in part). 

 Isocardia Markoei Conrad, 1845, Fossils of the Medial Tertiary, p. 70, pi. xl, fig. 2 



(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, 4G mm. ; diameter, 27 mm. 



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



Collection. — Maryland Geological Survey. 



Isocardia fraterna Say. 

 Plate LXXXV, Figs. 3, 4. 



Isocardia fraterna Say, 1824, Jour. Acad. Nat. Sci. Phila., 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 Conradi d'Orbigny, 1852, Prod. Pal. Strat., vol. iii, p. 121. 

 Glossus rusticiis Conrad, 1854, Proc. Acad. Nat. Sci. Phila., vol. vii, p. 29. 

 Bucardia fraterna Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 570. 

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

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



