146 University Geological Survey of Kansas. 



MACRODON. 



Lycett, Murch. Geol. Chelt., (1845). 



Macrodon sangamonensis ? Plate XX, figs. 2-2b. 



Macrodon sangamonensisWorthen, Geol. Surv. 111., viii, p. 123, pi. xxi, 

 ff. 3, 3a, (1890). 



Worthen's description : " Shell large, transversely elongated, 

 hinge line equal to about four-fifths of the entire length of the 

 shell. Posterior margin compressed and obliquely truncated, 

 so as to meet the hinge line at a rather acute angle ; posterior 

 extremity quite narrow and rounding gently downward to the 

 basal margin. Anterior margin regularly rounded from the 

 anterior extremity to the basal margin, which is slightly sinu- 

 ous about the middle. Beak depressed, strongly incurved, 

 placed about one-fifth the length of the hinge line from the 

 anterior extremity. A gradually widening depression extends 

 from the beaks to the posterior extremity on the dorsal margin, 

 and on this flattened portion six or seven strong striae may be 

 seen, which extend from the beak to the posterior extremity. 

 Strong lines of growth extend around the basal margin, and 

 minute transverse striae are visible under a lens, especially on 

 the anterior portion of the shell. Length, 2i inches ; length of 

 hinge, If inches ; height, ^~| inch ; convexity of the valve, T 7 6 

 inch." 



Range and distribution : Upper Coal Measures ; Turner (Wy- 

 andotte county) . 



It is with much hesitation that I refer these specimens to 

 this species, even provisionally. The specimens from Turner 

 are very closely related on the one hand to M. sangamonensis 

 Worthen, and on the other to M. striatus ( Schlotb . ) . They differ 

 from the former in not possessing minute radiating striae on 

 the anterior portion of the shell, but striae larger than on any 

 other part of the shell except on and above the umbonal ridge, 

 and in possessing a large shallow sinus with obsolete costae in 

 the central portion of the shell. It differs from M. striatus also 

 in the obsolete area in the central or sinuate portion of the shell, 

 and very markedly in the nature of the teeth in the front of 

 the hinge; in M. striatus (as represented by King) there are 



