CARBONIFEROUS AGE. 



33 



Myalina suhquadrata, 

 A. Outside of a left valve somewhat weathered. B. Hinge view of same. 



In size and general appearance this shell resembles Myalina suhquadrata, of 

 Shumard, to which we have concluded to refer it provisionally, on the authority 

 of Dr. S., to whom we sent the above cuts for comparison. It will be observed, 

 however, on comparing our figures with those of the typical specimen of M. suh- 

 quadrata, published in the Missouri Report, that our shell differs in having its 

 posterior margin curving forward above, so as to intersect the hinge (as may be 

 seen by the direction of the lines of growth) at an obtuse undefined angle, instead 

 of being nearly straight and intersecting the hinge at right angles. This peculiarity 

 gives a different expression to the posterior outline of the shell, that had led us to 

 think it probably distinct. Should it be found, when we can have an opportunity 

 to compare a series of specimens, that this difference is constant in adult examples, 

 the propriety of separating these two forms can scarcely admit of a doubt, in 

 which case the form under consideration may be designated as Myalina ampla. 



Locality and position. — Leavenworth City, Kansas, from a thin layer of impure 

 limestone near the level of the Missouri Eiver. Coal Measures. (Type No. 998.) 



5 April, 1864. 



