Beede: New Species of Fossils 



9 



the beak. The posterior flattening in these shells is rather small. Shell 

 thickening goes on to a considerable extent in the region beneath the hinge. 

 The platform for the anterior adductor attachment is small. The posterior 

 adductor scar is large, roughly ovate, rounded below, nearly straight on the 

 long posterior side, but it is notched on the upper anterior margin. Measure- 

 ments of seven specimens are as follows: 





1 



2 



3 



4 



5 



6 



7 



Length of hinge.. . 



37. 



39. 



34. 



36.75 



32.5 



43.5 



39.5 



Height of shell.. . . 



68.5 



73.5 



70. 



72. 



69. 



91. 



64.5 



Length parallel to 

















hinge 



43. 



41.5 



38. 



42. 



46. 



58 + 



39 + 



Height of hinge 

















plate 



10 -r 



14. 





10. 



10. 







Transverse diam- 

















eter 



24.5 





25.5 







29. 



28. 



Willard shales(?) ; Myalina cut, on Midland Valley railway, near Foster, 

 Oklahoma. 



The obliquity of the main axis of the shell, which is 10°, the convex 

 posterior border, and the short hinge at once separate this species from M. 

 suhquadrata Shumard. The small obliquity of the main axis of the shell 

 to the hinge line, the regular lamellae of growth, and its flatter appearance 

 at once remove it from M. kansasensis Shumard. It has relatively little 

 resemblance to the remainder of the species assigned to this genus. How- 

 ever, care is necessary in dealing with right valves of this species and M, 

 suhquadrata Shumard, since the right valves of these species fit into the 

 left valve and are flatter. Thus the right valve of M. suhquadrata has nearly 

 the same form as the left valve of this species. It is difficult, tho by no means 

 impossible, to separate them. 



Myalina bialata n.sp. 



Shell large, bialate above, more or less ovate on the ventral margin. 

 The hinge is very long; the beak and posterior extremity are greatly produced 

 in adults so that the ventral part of the shell has somewhat the appearance 

 of a sack suspended obliquely fro n the long hinge. Both the anterior and 

 posterior margins retreat below the hinge, producing strong concavities 

 in the outline of the shell. If the lines of the sinus below the beak, and the 

 one below the posterior part of the hinge, were produced, they would cross 

 nearly at right angles just below the center of the shell. The shell of the 

 beak is greatly produced beyond the terminus of the umbones within the 

 shell. In some instances this prolongation of the beak beyond any cavity 

 in the shell equals nearly a third of the length of the hinge. In like manner the 

 posterior prolongation of the hinge beyond the body of the shell may, in 

 some instances, be nearly a fifth of the length of the hinge. The main axis 

 of the shell has an obliquity of about 15° to the hinge line. The body of the 

 shell in the ventral region possesses a somewhat ovate curve, the posterior 

 part merging with the very gently convex posterior margin until it approaches 

 the hinge, whence it curves abruptly backward and then upward and finally 

 a little forward to the hinge. The anterior margin is somewhat broadly 



