14 



fades away Ijelow nml is lost in tlio ^eneial couvexily of the eLclI. 

 Tlie wing is suinll, Hat and lias an acute estroniity. Shell marked 

 with distant concentric lines of fj;rowth. 



All of our specimens are casts of the left valve, no part of the 

 shell is pr(!8erved, and no radiating lines are digcernahle. 



Tbis tpecies is distinguished by its oblique, elougate-ovate form 

 and small posterior wing. 



Found I'y Miss Jessie Blair, in the Chouteau limestone, near 

 Sedalia, Missouri, and now in the collection of S. A. Miller. 



Family MYTILID.E. 



MVTILMiC.V JKSi^IE.i;, n. S|). 



I'ldfc II, Fi(j. 1, left valve ncurhj cotiiplelcj Fiij. :.', (luoihcr left 



vnloe with more of ihe (interior end broken off"; Fig. 3, part 



of (mother left valve; Fig. i, (inferior end of right valve 



cowplefe : Fig. 5, anterior end of left valve complete, 



small sj)erimen . F^ig. (!, part of the surface 



of the shell magnified four diameters. 



Our specimens are quite variable, from medium to considerably 

 above medium in size. 



Shell oblique, elongate, subelliptical, with venticose valves in 

 middle part, where it is subcylindrical. The diameter through 

 the valves in the middle area, is nearly equal to the distance 

 from the hinge to the basal margin. Posterior end of the shell 

 cuneiform and narrowly rounded. JJiisal margin of the shell 

 oblique, nearly straight or slightly arcuate. Hinge line about 

 half the length of the shell, slightly arching. I^osterior to the end 

 of the hinge, the shell is slightly arcuate until it adruptly curves 

 into the pjst-basal margin. Beaks obtuse ami terminal at the 

 anterior end. Umboaes high and abrup'ly roumled to the hinge 

 line, posterior to which the uiiibonal slope merges into the cuneate 

 form of the shell. Surface markeil by concentric lines of growth. 

 Shell thin. 



This species is readily distintiuished by its general elongate 

 form from all oth<M'?. We have nunjerous fragments of this spec- 

 ies but most of them are caste. Part only of the shell is preserved 

 ou a few of the fragmeuts. 



