IBID) DOA IIE Ee 
TIN GULAGSLYUILOIDRA ee cemel ane smoaainecc.or oc won cinwaslcccneacc ccsses Been costes So ceeee eae 
Fig.1. View of a specimen from the lower portion of the Carboniferous formation, north of 
Pinto Peak. 
DISCINADN E WiBIERE Vikse oe a see rose cas poco cee ciccc ase cancec succeed so teek ctcetoe snes access 
Figs. 2, 2a. Dorsal and ventral valves of a form from the shale in Secret-cafion-road Cafion, 
doubtfully referred to this species, enlarged to two diameters. 
3. Dorsal valve from Richmond Mountain. Natural size. 
SEL ERE AG MALLE Wee ene ee ete eee a aae setter Sate eines niet wives lnraisinialc snislccels eile ste s,c.cie siemicen sles scice 
Figs. 4, 4a. Dorsal and ventral views of the average size specimens found at Richmond 
Mountain. 
DED ARES URS UE Ae ey ene ae eee olnieie ales Siem a cineln cia mice a wa icieiaw else leis pele odie aan eae ae ewan 
Fig.5. Dorsal view of a specimen from Coal Hill, Pancake Mountains, White Pine County, 
Nevada. 
CEMARGEHORTA C OOPERENSIS) ose men see ee ee inn sane lelaeici sia onic Menwle= ce caicis sie A> - oman 
Fig.6. Ventral view of a specimen from Richmond Mountain. 
PS BER DEE RAR ANNINGE CLUAENS siete es arte la wie ene aaa sat nlwlaiatelale\= miele talala a'ciolaisintnian! eles > «ina = 6=) o1nteieieleien == 
Figs.7, 7a. Dorsal and ventral views, showing the rounded cardinal extremities, and the 
coarse plications, 
RERVINCHONE ZANE UH KIGNSIS =. stele saaiee cesta = aia a ele csinellela'a eve ntatelelstalal~'ela:almiaiels eoi=\vlne  wicinivteinininwieo = 
Fig. 8. Lateral view of a specimen which is slightly crushed. 
8a. Ventral view of the same. 
8b, c. Ventral and dorsal views of a smaller example. 
iNnnaniis) IRORESH Et 55.22 sear Ses oS Soone a eecoes SoeEboonessoood= Sobedose pbs Sae soesaeiedod cee sees 
Fig.9. Dorsal view of a specimen from the cafion north of Pinto Peak. 
9a. Lateral view of the same. 
(Saag TOI. CISTI TO Cp oe os BAS CO b Ca DEER Code Ser SE eased e CEO COE RSOD COO MO So IOOCO DS SeCOmeseer 
Fig. 10. View of a ventral valve, from Richmond Mountain. 
(S/DERTIAIIE A, DIMMED SV IS) eS o5 9566 coe ors cope ee es Eee aS 59 ca Scoe Sees SHE Hee oHeeeeoesees ees 
Fig. 11. View of a ventral valve, from which the outer shell is largely removed. 
(STRATOS, CIPI GY en meg coceos Socoos SEE SEO BOC ESS OSCE Ss BEDS OSUDSoSaes Coes eosEeereecps 
Fig. 12. Dorsal view of a specimen from the Chester limestone of Chester, Ill. Introduced 
for comparison. 
13. Same view of a specimen from the upper portion of the Carboniferous Group in the 
Eureka District. The spine bases are not shown in the figures, although quite 
prominent on the shells from each locality. 
SItTRMP TOR EAN © HES (ORION IS UREA senna seeee saa lancet emateletetnela= nislceninleini= sais alent sia n'=eln merino = 
Fig. 14. View of a strongly striate form, found at Richmond Mountain. 
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