l.AMl.t.l.ll i: \N 111 



:ie mii-cul., ,if moderate -i/e ;iiitl fulliK--. incurved, the 



half slightly flattened in tl; Tin- flattening, which i- produced l.y tin- u-ual 



internal thickening of tin- anterior part of the shell, extends obliquely liarku 

 and i|nwn\\arl fnuii t! .ward the middle of the ventral edge. Ant. 



mii-cul;. -..niewhat uniform, not a- sharply delined I.elou a- i> u-ual fur the 



genus, very di-tinct. 1, . and parth ..pped above liy the tilling of the 



beaks. I'allial lint- .-harp in tln> antt-rior two-lift \\-. nl.scnrc Ix'hiii.l. I ' interior 

 miiM-ular inipn^mn t<m light to be determined with certainty. Hinge plate nar- 

 with t-. :! liori/.nutal i'i-terinr lateral teeth in the left valvo and thn-e 



in the right. Cardinal teeth unknown. 



Tin- -|>ecie> i- u>-. \ith several of l'>/i-fil,nifn that, under ordinary condi- 



tinn-, ai -ily di-tingni-hed. The feature to be chiefly relied upon in separating 



them (/. r of the anterior niu-mlar scarl i- ii-nally oli-ciired l.y 



talli/ed remnants of the shell. When these are iviii"\ed ami a clean .-a-t of the inteior 



i't'on produci'd the ditiiculties will have been overcome. -ince the I <i>iu.r, ////./ ma\ 

 then lie di-tingni-lied at mice from th- / hy the much greater di-tinci 



and ch;i .f the anterior mu-ciilar -car. (I'omp. ligs. :{ and 4'J on plate xxxix.l 



Form-itinn and foou/rty. Tr.-nt<.n lln >, Minn. 



Mut. Reg. No ^HT ? 6 1. > 



us MATH KIM A. Billings. 

 ltatlirri.1, liM <*. Can. Nat. and Oeol., vol. Ill, p. 440. 



il eijuiv .-ry iiieipiilateral, oblong (juadrate or suboval; I mil 



anterior. Surface marked with concentric growth lines only. Hinge of moderate, 

 strength or rati. ,. with external linear ligamental area posterior to the beaks, 



two small, divaricating cardinal teeth beneath the beak of the left valve and only 

 one in the right: no lateral teeth. Adductor impre--ion-.two; the anterior one 

 -mailer and better defined than the po-terior. I'.illial line simple, obscurely defined. 

 Type: Miitlii-riu h-neru Billings. 



Only four or five species known to me have the characters of this genus. They 

 are all small shells and with one exception belong to the Trenton. .!/. tenera is from 

 that hori/.on in Canada, one or two mi.le-cril- r in Kentucky, and M. 



M Minnesota, while ti. Hall, which i- a true Mntli. 



belongs to the Niagara of \Vi-con-in and lllinoi-. 



M \i in - <'<//. 



-v UK! ao. 

 heria ntyota TI.KK n, l-nl 



II large for the gen lal. wide-t pn-teriorly. with ti 



terminal, small, incurved, projecting -lightly al- a stroi . 



