

689 



sometimes thicker at one end tlian the other, ami the depre- t -ulci l>etween 



tin' ridges relatively narrow. These specie- pa over into, ami tin- -ection ought to 

 i nclu. It', some of tin' -n-called i|iiadri j y //<// /,r.* Their relation-; to Titrn<lrll<i 



will he considered in the remark- under that genus. 



lloi.i.i ^ -i i \. it. ap. 



<*.*-*. 



.:.: tiik'ht." :<> nih -- D.L'I: mm. 



.111 

 .in. 



Vahes compre--e 1, suhovate in ontlii _rlit aliove; length of hinge some- 



what \arialde. shortest, apparently, in old examples; dorsal angles more or less 

 distinct : edge- of valve- thirk. forming a >harpl\ --detined. thin marginal ridge; inner 

 ridjre thin, rather lon^. l"-shaped. one of the arms with a slight swelling near or at 

 ita upper extremity: Mirfaee lietween the ridges Mat and without ornament. 



The small valves of this >j>ecies remind -omewhat of ' imminln, hut as that, 



form ha- no inner or horseshoe ridge they are distinguished very easily. 'l>lr<i>l,-ll,i 

 <jit*lnlir<il<i is a larger form and ha- the inner ridges joined below with the marginal 

 ridge. The nean--t allie- orrur in the Upper Silurian deposits of Kurope, but it is 

 distinet from them all. 



Formation and locality. Galena shales (CllUmbonltes bed), near Cannon Falls, Minnesota. 



IloI.UA r.Viil I.UIDKA, II. 8p. 



PI \TK xi. vi. nos. n-a. 



'. i". nun.: hi^'ht n.l mm.: t hi.-kiiejMO.35 mm. 



Valve- -nl.ovate. with e(|iial rounded ends, a rather short, straight hinge, and 

 illy defined dor-al angle-: marginal ridge thick, rounded, a little wider at one end 

 than at the other: inner ridge -trong. one end swollen, the other small and failing 

 '" reach tl i edge; interspace between the two ridges very narrow. 



;on of .evcrml very doubtful *peclf dawribed by Know, the known (pecle* fill i,,i., tbM weUoe* 





Mono* - 



2. 



B. pvmO.1 

 II. . 



Una J. an.) II 

 111. intti-i<i,4:i Jnoiw. I' 



..II JUIMM. I 



B. oU*a rirl.-h. Dev. 



ii. m attfa i Ulrtcb. I ci 



H tw/.r.^if 



II. rlnrt <rmr. mUui J. an. I II 



,rurul,lrf \ 

 II. xjun.kll 



ii HM|*MM i r t, i. -.. 



B. rrvuLirti F.mmon. - 

 B. penttleata r:- 



B. duptrs Kr..u 

 B. ^mm^rir.1 II a. 

 UryrVAki rinrfct Jontw. I 

 B*vrteMd Ita0 Joow. I 

 B. irnjula Joncv Dr T. 

 ./". Ml i' ! i -i - !> 



J, Mi K - 



