276 PALEONTOLOGY. 



Formation and locality. — In limestones of Permo-Carboniferous age, foot- 

 hills southeast of Salt Lake City, Wahsatch Range, Utah. Collected by 

 S. F. Emmons, esq. 



MYAT.INA PERMIANA. 



Plate VI, fig. 7. 

 Mytilus {Myalina) Permianus Swallow, Trans. St. Louis Acad. Sci., vol. 1, 1858, p. 17. 

 Mytilus (Myalina) concavus (Swal.) Meek, ib., p. 18. 

 Myalina Permianus (Swal.) Meek, Pal. Missouri, p. 62, pi. ii, fig. 7. 



Shell of medium size, elongate triangularly-ovate, much higher than 

 long, suberect; hinge-line shorter than the width of the shell below; ante- 

 rior margin concave ; base sharply and narrowly rounded; posterior margin 

 broadly rounded, sloping abruptly forward in the upper part to meet the 

 hinge-line, considerably contracting the length of the shell at this point. 

 Surface of the valves highly convex near the front border, and somewhat 

 gradually sloping toward the posterior margin; umbonal ridge rounded; 

 beaks obtuse, nearly or quite terminal. Surface of the shell marked by 

 concentric lines of growth, obscurely preserved on the casts. 



This species differs from the last (Jf. aviculoides), with which it is asso- 

 ciated, in the less convexity of the valves and more rounded umbonal ridge, 

 as well as in wanting the narrow and prolonged beak of that species. The 

 example used and figured differs from those figured by Mr. Meek (loc. cit.) 

 only in having the hinge-line a little shorter. This feature, however, varies 

 much among the specimens in the collection. 



Formation and locality. — Occurs with the preceding. 



Genus SEDGEWICKIA McCoy. 



SeDGEWIOKIA ? CONCAVA. 

 Plate VI, fig. 3. 

 SedgewicMa ? concava Meek & Hayden, Pal. Up. Missouri, p. 41, pi. 1, fig. 8, 1864. 

 I/yonsia concava M. & H., Trans. Albany Inst., vol. iv, March, 1858. 



Among specimens on a yellowish-brown sandy shale from the Wahsatch 

 Mountains, near Salt Lake City, is one so nearly resembling the figure cited 

 above that we cannot hesitate in considering it as specifically identical. 

 The specimen is about one-third longer than the figure cited, being about 

 nine-tenths of an inch long. The form is transversely elongate-elliptical, 



