K <>1A. 



of lobes terminating in ;i thin. Mat ..r rai-ed. horder. supported in the hinder part l.y 

 .idi-tant rii N, tliu- forming a- man) -mall cavities in the posterior 



edge of each valve; surface -mooth. 



Tlit- -mall cavities in the po-terior half of the edge remiinl of '/'<//< /'////<! ^umh'i- 

 linit'i. luit here the rc-eniMaii far they are widely dillerent in all other 



'I'lie-e c.mtie- and the relative nanowne of the posterior Imlli. together 

 with other peculiarities. di-tingui-h ' .'</ from ('. iluri/i Miller -p. . a Cincin- 



nati .-pecie- that re.-emMe- fig. s more clo-eiy than doe- any other one of the genii-. 

 When however it com. 'ion-hip, the next to be described is doubtless 



the nearest. 



Formation ami lix-alily !'||r thinl <if tin- Tn-ntnn ^hale* (Phyl!i>p<irlnu U-l), SU Paul and Can- 



ii"i. ta. 



"i.niNA <-I;A--A I'liirh. 



I'l.ATK XI. IV. Klli.-v IS-W. 



Jon : l.l, ii, I-'.H). Jnur : : 



l.i-tik;ili " ''I HUH . hi^lit ii tKiiniii : thicknettiO.60 linn. 

 -th ii "xi nun ; hlKlit 0..'>J nun : thirkrn-s> n.4i> nun. 



This species is closely related to ('. riilinitn. and \\ hen the edges are obscured l>y 

 the matrix, it is difficult to distinguish from one of the varieties of that sp<-' 

 But w hen the posterior edge is visible the difficulties vanish, there being no support- 

 nor cavities in the thick edge of C. crassa (compare tigs. 13 and 1G with fig. 9, pi. 1 1 i 

 Aiming other differences I may mention that in ('. i-rnssa the valves are constantly a 

 little smaller, the sulcu< wider, and the lobes more prominent, especially at the 

 ventral edge. The lobes are also more compact and ridge-like, producing an effect 

 that reminds so much of the "horseshoe" ridge of Jonesella. that I at first regarded 

 the species as belonging to that genii-. Hut that was before I knew of its close 

 relation-hip with <\ I'n 



.11. AMOClal<tl with Hi- ; 'lilrili.fl! > HlialtW at 



' IHIi'SOU. 



n CEBA.TOP8I8, n. . 



T.tr,idrlla (|..i ll.I'W). J.n. Hi 



Beyrichia (part.) ! : me! Wmi SK>. ;IIK| ..Hi. r :nni. 



Valves somewhat (.l)li.|iifly <nlovate. widest : iy.witli 



a thick rounded semicircular marginal rid^'r. and two .-nlnnediiini ridges extending 

 obliquely upward from the marginal rid^e. the anterior one reaching t he dorsal edge, 

 the other shorter and -mailer: p<-t-dor.-al end of marginal ridge raised into a 



