570 - PALAEONTOLOGY OF ILLINOIS. 



MACBODON TENUISTRIATUS, M. and W. 



PI. 26, Fig. 4. 

 Macrodon tenuistriata, MEEK and WOKTHEX, 1807. Proceed. Chicago Acad. Sci., Vol. I, p. 17. 



SHELL small, rhombic-oblong, rather distinctly convex 

 along the unibonal 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 middle; cardinal margin straight, not quite equal- 

 ing the greatest antero-posterior diameter; anterior side 

 rounding up from below, so as to meet the hinge nearly at 

 right angles; posterior basal margin narrowly rounded; 

 posterior margin obliquely truncated, ofte'n a little sinuous 

 above, dorsal region behind the umbonal slope compressed ; 

 beaks convex, a little flattened, incurved, rising somewhat 

 above the hinge margin, located about half way between 

 the middle and the front; flanks broadly impressed or con- 

 cave from the umbonal regions obliquely backward to the 

 faintly sinuous part of the base ; cardinal area unknown ; 

 posterior linear teeth about three ; surface ornamented with 

 distinct marks of growth, crossed by radiating markings, 

 w r hich, 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 striso. 



Length, 0.75 inch; hight, 0.31 inch; convexity, about 0.30 

 inch. 



Position and locality Upper Coal Measures j Springfield, Illinois. 



Genus AYICULA. 

 AVICULA MORGANENSIS, M. and W. 



PL 26, Fig. 14. 

 rtcria (1'terinea) Morganensis, MEEK and WORTHEN, 1866. Proceed. Acad. Nat. Sci., Phila., p. 259. 



SHELL (left valve), exclusive of the posterior wing, ob- 



