I.AMKI.I.ll.i: Uf< HI \ 



M .llolop.1. n.n. I 



as the shell: anterior end very small, sharply rounded ,i!ve, curving backward into 

 the slightly convex, medially almost straight. li;i>al margin; posterior edge gently 

 curved, truncate, nearly vertical. strongly convex below; above turning abruptly 

 into the hinp> line. Beaks small. Imt little incurved. not prominent, about one- 

 sixth of the length of the shell behind the anterior extremity. I'mbonal ridge mod- 

 erate. cardinal slope flat or slightly concave, ventral and anterior sin]*'- depressed 

 convex. Surface marked with distant strong concentric lines of growth, and between 

 these with a liner set. In casts of the interior the anterior muscular impression i- 

 well marked, not very largo, vertical, situated in front of the beaks and close to the 

 cardinal margin. A little more than one-third of the scar is divided on" above I 

 distinctly impressed transverse lino. Posterior scar indistinct, much larger than the 

 anterior. -it uated behind the center of the posterior cardinal slope. Pallial line simple, 

 rath'T'li-tmct, not following the outline of the shell, being farther removed from the 

 margin in the postero-basal region than elsewhere. Hinge as shown in figure 28 on 

 plate xxx vi. Free casts of the interior of both valves, being without the hinge 

 plate, are longer in proportion to the hightthan are the impressions of single valves. 



The shape of the shell will distinguish this species at once from all Minnesota 

 Lamellibranchiata except Mnthrria rugosa and Cyrtodonln n finis, both of which occupy 

 a higher horizon and have a different shell structure. 



I have before me ten more or less complete silicified shells from the middle Tren- 

 ton or "Orthis beds" of Tennessee and Kentucky. These belong to a species that is 

 closely allied to K. plnnn and which may be called Kunjmya subplana, n. sp. The n-u 

 species does not attain the size of the Minnesota form, and is not so high and more 

 oblique posteriorly, while the margin is le-- narrowly rounded in the postero-basal 

 region. The Cincinnati species, E. alutu (Modiolopsit alata Ulrich) is a slightly 

 shorter and more compressed shell, with a more convex ki-al margin and ditlerent 

 anterior muscular scar. 



formation and locality. Lower limestone of the Tn-nt4.ii formation In Minnesota at Minneapolis, 

 ml and Cannon Falls. In Wlsc<>n-iri the special seems to be restricted to the "Lower 

 limestone at Janesvllle, Beloit and >I int. 



-Uu ... 749, 757, SOU. V)12. 5013, M82, 6368, 5869. 5834, 8312. 



,1> AUTIHOMVA, II. grn. 

 Modiolopdt (part), of various authors. 



Sh.-H ovate, more or less elongate, narrowing anteriorly. Valves moderately 

 ventricose, fitting each other tightly. Anterior end short, l.nt not excessively go. 

 Base gently convex, occasionally straight, never sinuate. Mesial sulcus want; 



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