120 LAMELLIBRANCHS. 



Macrodon tenuistriatus MEEK <fe WORTHEN. 



Area striata Geinitz, 1866: Garb, und Dyas is Nebraska, p. 20, tab. i 



fig. 32. (Not Mytilites striatus, Schiotheim, 1819.) 

 Macrodon tenuistriatus Meek & Worthen, 1867: Trans. Chicago Acad. Sci., 



vol. I, p. 17. 

 Macrodon tenuistriatus Meek, 1872 : U. 8. Geol. Sur. Nebraska, p. 207, pi. 



x, figs. 20a-b. 



Shell small, rhombic oblong, rather distinctly convex, 

 along the umbonal slopes, and near the front a little more than 

 twice as long as high ; basal and cardinal margins parallel ; 

 the former nearly straight, or somewhat sinuous near the mid- 

 dle; cardinal margin straight, not quite equaling the greatest 

 antero-posterior diameter; anterior side rounding up from be- 

 low so as to meet the hinge nearly at right angles ; posterior 

 basal margin narrowly rounded ; posterior margin obliquely 

 truncated, often a little sinuous above ; dorsal region behind 

 the umbonal slope compressed ; beaks convex, a little flattened, 

 incurved, and rising somewhat above the hinge margin, located 

 about half-way between the middle and the front ; flanks broadly 

 impressed or concave from the umbonal regions obliquely back- 

 ward to the faintly sinuous part of the base; cardinal area un- 

 known ; posterior linear teeth about three ; surface ornamented 

 with distinct marks of growth crossed by radiating markings, 

 which on the compressed posterior dorsal region form rather 

 well-defined radiating lines ; anteriorly, however, these diminish 

 in size so as to become very minute or scarcely visible, crowded, 

 obsolescent striae. ( Meek.) 



Horizon and localities. Upper Carboniferous, Upper Coal 

 Measures: Kansas City. 



Macrodon obsoletus MEEK. 



Plate xlvi, fig. 1. 



Macrodon obsoletus Meek, 1871: Rep. Reg. Univ. West Virginia, p. 5. 

 Macrodon obsoletus Meek, 1875: Geol. Sur. Ohio, Pal., vol. II, p. 334, pi. 



xix, fig. 9. 

 Macrodon obsoletus Keyes, 1891: Proc. Acad. Nat. Sci., Phila, p. 249. 



Shell considerably larger than M. tenuistriatus, and with the 

 radiating lines poorly defined or absent. 



