MAEYLAND GEOLOGICAL SURVEY 363 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 TJ. S. National Museum, Philadelphia Academy of Natural Sciences. 



Subgenus MYTILOCONCHA Conrad. 



Mytilus (Mytilgconcha) incurvus Conrad. 

 Plate XCVI, Pigs. 2, 3, 4. 



Myoconcha incurva Conrad, 1839, Fossils of the Medial Tertiary, p. 3 of cover of 



No. 1 ; p. 52, pi. xxviii, fig. 1, 1840. 

 Mytilus incurvus Conrad, 1854, Proc. Acad. Nat. Sci. Pliila., vol. viii, p. 29. 

 Ifytilus {Myoconcha) incurvus Conrad, 1861, Fossils of the Medial Tertiary, No. 4, 



p. 88. 

 MytiloconcJia incurva Conrad, 1862, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 291. 

 Mytiloconcha incurva Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 579. 

 Mytiloconcha incurva Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 7. 

 Mytiloconcha inc7-assata Whitfield, 1894, Mon. xxiv, U. S. Geol. Survey, p. 38, pi. v, 



figs. 10,11; not of Conrad. 

 Mytilus (Mytiloconcha) incurvus Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, 



pt. iv, p. 789. 



Description. — " Shell incurved, thick, narrowed toAvards the apex ; 

 posterior side with a submarginal furrow; hinge with a narrow straight 

 groove for the cartilage, and a l)road furrow on the posterior side." Con- 

 rad, 1839. 



This shell is heavier, more sharply curved, has a longer and more mas- 

 sive cardinal area and more nearly equidistant dorsal and ventral mar- 

 gins than M. conradinus ; teeth strong, two in left and one in right valve, 

 becoming obsolete in old age. As the cardinal area increases in length 

 with growth the teeth are jorolonged apically as ridges with a furrow on 

 each side; area otherwise flat except for a marginal ligament groove ex- 

 tending along the posterior side of the area to the apex. 



Length of imperfect valve, 120 mm. ; width, about 35 mm. 



Occurrence. — Choptank Formation. Greensboro, Cordova, near 

 Skipton, Dover Bridge (Dall). Calvert Formation. Church Hill, 

 Truman's Wharf. Also at an unknown horizon in Calvert County 

 (Conrad). 



Collections. — Maryland Geological Survey, U. S. National Museum, 

 Philadel2:»hia Academy of Natural Sciences. 



