FOSSILS OF THE CAKBONIFEKOUS. 



237 



Genus MYALINA De Koninck. 



Myalina congeiieris, n. sp. 

 Plate xix, fig. 6 ; plate xxii, fig. 10. 



Shell oblong, the height being twice the width even in the broad ex- 

 amples; hinge line straight and ranging at an angle of 60 with the nearly 

 straight anterior margin; base narrow, but rather broadly rounded, poste- 

 rior very broadly rounded, curving slightly inward towards the cardinal 

 line. General surface of the valves strongly convex towards the front 

 border, and beaks becoming more depressed on the posterior portion. Sur- 

 face of both valves marked by slightly imbricated lamellae of growth. 



The specimen illustrated is more narrow than a right valve associated 

 with it that has all the essential characters of the species. Its specific rela- 

 tions are with Myalina angulata M. and W. (Geol. Surv. 111., vol. ii, p. 300), 

 from which it differs in having a more obtuse angle at the union of the car- 

 dinal and anterior margins and a less oblique anterior margin. It is in out- 

 line intermediate between M. angulata and M. subquadrata Shumard (Geol. 

 Surv. Missouri., vol. i, pt. 2, p. 207, 1855); Myalina Apacliesi Marcou (Geol. 

 N. Amer., p. 44) may possibly be a closely allied species, but with the descrip- 

 tion and figure given by its author this cannot be determined. Compare, 

 also, M. St. Ludovica Worthen (Geol. Surv. 111., vol. v, p. 540). 



Formation and locality. Lower portion of the Carboniferous Group, 

 on the wst slope of Richmond Mountain, Eureka District, Nevada. 



Myalina Nemesis, n. sp. 

 Plate xix, fig. 5; plate xxii, fig. 7. 



Shell subovate to subquadrangular, depressed convex, base broadly 

 rounded; anterior margin slightly concave or straight, posterior outline 

 broadly rounded and meeting the hinge-line at an obtuse angle. Hinge 

 straight, shorter than the greatest width, and ranging at nearly right angles 

 to the longitudinal axis of the shell. Beaks terminal and directed obliquely 

 forward. 



