FOSSILS OF THE COAL MEASURES. 575 



Genus MACRODON. Lyeett. 

 MACRODOX DELICATUS, M. and W. 



PL 26, Fig. 3. 

 Maerodnn defkmtu*. MEEK and WOKTHEX. 1670. Proceed. Acad. Natural ScL, Phila., p. 40. 



SHKI.L small, about twice and a-lialf as long as high, 

 moderately convex, elongate rhomboidal in outline, poste- 

 rior margin obliquely truncated, so as to be angular at the 

 base: cardinal margin about three-fourths the entire length, 

 and nearly parallel with the base; anterior extremity very 

 narrowly rounded: basal margin nearly straight along the 

 middle, but rounding very gradually upward anteriorly; 

 beaks depressed, and placed about one-fourth the entire 

 length of the valves behind the anterior extremity ; poste- 

 rior umbonal slopes subangular from the beaks obliquely 

 backward and downward, to the sharply rounded or snb- 

 angular posterior basal extremity, while the spaces behind 

 and above these slopes are compressed or slightly concave. 

 Surface marked by small ridges and lines of growth, which 

 are crossed by raised radiating lines or linear costte, rather 

 widely separated posteriorly, but more closely arranged, 

 and less strongly defined towards the front part of the 

 valves. (Cardinal area, hinge and muscular impressions 

 unknown.) Length 0.45 inch; hight, 0.19 inch; convexity 

 about 0.11 inch. 



This little shell will be readily distinguished from its associate, for- 

 merly described by us under the name Af. tenuistriatiiSi by its much 

 more oblique and less gibbous form ; but more especially by having its 

 linear radiating costa? separated by wide intervening spaces, instead of 

 being closely crowded together. We know of no species with which it 

 could be confounded. 



Locality and position Springfield, Illinois. Upper Coal Measures. 



