420 



niOVKEDlNUS ()!'' Tllli NATIONAL MVSEIM. 



I'agc. 

 Oholiis ( l/uifiiililla) rrldluM N'ollioitli :58r> 



Vlfi. I. Iiiloiiiir olii voiiliul \■lllvl^ Inuii llm rpiiir (Jaiiilniiiii MlnitM, iiuiir .Ir^olnclil. 

 '-'. IntiM-ior ol'tlDi'Hal valvo, hhhocjiiUmI with lljj- !■ 



Ohohts <ii)<)lli)iiK I'lii'liwald 385,391 



Fif;H. ;t-ti. InliM-i(ir of tlio iioatorior iiortioiiH of four ventral vuIvhh from KHtlaiid. Tlio 

 variation in form and jtuHition of t lio niuHcIo ncixvn is well Hhuwn. 



I'l.ATK XWU. 



>/. ITinboiinl. 



c. 'rraiiiizoidal ariia, including (^oiitral 



tiviwx, niiddlo and imlMidn lalirals. 

 1,1. I'rdi.liv 

 h. <!(ttitral. 



I. 'rransnii'dian. 



/'. Anterior lateialH. 

 A-. Mi<ld(« lal.<ralH. 



I. Oataido latoralR. 



/). I'(>di(do K''""^'*'- 



((. (JiMitnil liilcral spat-o. 



a'. Outor lati'ral npaot^ 



./'. Klcxiiri' lines. 



I ». \'aHcnlai' MinuH. 



//*. I';iri(t;il lianil. 



r. Vinccrnl lavity. 



l*a;;o. 



Ohohis ( LiiH/iilella) daviHi Mo( 'oy . , :5!tl-4 



Vifi. 1. Cant of intorior of a llatlont'd ventral valve (x H). iirrservinn nearly the normal 

 ontlii f tlio hIu'H. 



'2. ('axt of interior of a tiatteniid and distorti^l ventral valvi>, in » liicli i)in vascular 

 rtiniiH«H and viscoral cavity are fairly well indicated. 



;i. Cast (d' inlei'iorof tli(< jiostorior i)ortion of a ventral valve (x It), drawn In illus- 

 trate the iimhonal and pedicle l^UHcl(^ HcarH. 



4. Cast of interior of dorsal valve (x :)). 



.1. ("a.stof interior id' a dcMV-^al val\ c loM;;iludinally sliortentMl by compresMion. 

 Krom the Lin;;;iila Kla^js at- the typical locality— Port Madoc, Nortli Wales. 



OhoUiK ( />. ) (tviilaiiiiiihi.s KdtMiicr 392-4 



t>. (^ast of interior <d' ventral valv(<. frmii the Up]H^r (.'amlirian, Llano Cuunty, Texas. 



ri.ATic xwiii. 



(J. Ihnhonal. 

 til. I'edicle. 



c. Trapezoidal area, iiieludiiiK i^i'ntral 



scars, middle and outside later.ils. 

 /(. Central. , 



I. Transmedian. 



/. Anterior laterals. 



I. Outside laterals. 

 p. I'l'dielc f;i'oo\ e. 



./'. i''lexiire lin((s. 



I'n. Vascular sinus. 



/'«. Parietal haml. 



IK N'isceral I'avity. 



.r. lleart'Sliaped cavity. 



«. Median st<ptum. 



z. Tialeral liriiiiclies of tln' vascular system. 



II. Supposed aeeideiilal luarkin;!. 



Pago. 



OboliiH ( L. ) aciitaiKjiiliiH Kot'incr 3!I2— 1 



Kiy;. 1. Oast of interior of venlial valve (x II). This is a htvaulilul specinu'u from the 

 I' ppi^r (Cambrian, I.lano Oounty, Texas. 

 2. ('a>t of interior of dorsal valvu (x 5) and outline of siiei^imeu as.socialed with 

 liK- 1. 



Obolim (/-.) tiiiiplii.s Owoii ;{!)2~1 



;t. Castof interior of ventral valve from tlu> Middh* ("ambrian santlsloiie at Dakota, 



Minnesota. 

 4. Cast of dorsal valve associated with lin- •'• 



(HioliLs (/,.) Vila Ijjill iiiul Wliitliold 



390 



f). Cast of inlt<rior of ventral valv(( from the Middh< C'aMd)rian shales, near Helena, 



Montana. 

 C. (Inst of interior of dorsal valve associated with lij;. T). 



7. Cast of interior id' vejitral valve from the Middle Cambrian shales of ICast Can- 



yon, Oiiuirrh Mountains, Utah. 



8. Cast ol' interior of dorsal valve from the Midilh' Cambrian shales, near I'ioche, 



Nevada. 



