- ?93 - 



as ■fc'i^ei' pass over the "boclj' rins (as n.sual in Oarci. i Tim ) are co" 

 to^.'ard the iirahones. '.VehrL this coatir.?' is oy v;ear the top 



of the '"ih r/i 1 1 hf^ "lat a': ' '^-'^ v7hile their si'^^G shov: frin'"'- 



iiig v/rinkles. If erosioia attack the ' "aee, the structure 



of the shell ^- '-eed loops 



of the origins! outer coat." (Dall, IDCO). 



S'r.ell of raediiiia jiiae, tliin, v/ell inflated, suhequilateral, 

 "broadly suhovate in oiitline, ''±-e crrve of the anterior '-largin heir:^ 

 sli-frhtly more eonvp" t>'an that of ^""'0 ■■^octerior iiiargln; umhones 

 lOT.'; extenial surface of adult shell sculptured \7i th fort^ or 

 forty-one narrow, lo^, siihroimded radial rihs separated by usually 

 vovy narrov; interspaces, anterior ten to thirteen rihs o ' ? ^ntecl 

 v-1 th transverse or slightly o"bliq.ue nodules, posteriorly cho nod- 

 ules progressively confined to the distal end of the rihs; to- 

 ':jc^^ -- ^> '-enter of the shell the -'■'i'-'- "':<ocoining slightly ner'^^'-;- 

 e-r, these rihs, as well as the non-nodulated portioiis of the 

 anterior rihs, crossed hy fine, arched concentric strige, the 



12 r\;'^T cy c- -' r1 g q -p -*-"- .'r, -j-rn''- >,.•:: ' ,t -^ ' yo •-• -^^ ^ ^ -"- T^h in th C 



interspaces the conce^.^rio tjtriae in'..'onspicuoLis ; toward the p'-;. t- 

 erior end the similarly sculp' ' • hroader a 



interspaces wider; the e-' "■■'"'" posterior rihs lower ancl smooth, '^" - 

 cept for a rovr of distant, fine, r ' ' -;Tly sh^rp nodules on 

 their posterior edge; upper posterior rmrgin of the shell foeh- 



