- !^97 - 



Shell m Oder at elj" large, solid, long-itudinallv sulDovate, 

 deciderll"" inflated; upper portion of the aiiterior lateral niarrrin 

 ohliqaeli' sub truncated,. Icu'ver portion rounding ''oroa'"ll^' into the 

 gently arcuate "base; Kiedian portion of the posterior margin 

 suhtrinc ated or scarcely curved, the suhtnmcation extending lov/er 

 than on th-: 'srior side and joining the base more abruptly; 

 uinbones high, prominent; eytericr surface sculptured with 

 thirty-one to thirty- three strong radial ribs re-oarated by 

 narrow, deeply channeled interspaces; five aii'cerior ribs bear- 

 ing medially situated, disconneoteci, globi'tlcr nodules, sorae- 

 tines absent from the broader distal half of the ribs; the next 

 sizteen or seventeen ribs ernamented v/ith a ra,ised frill placed 

 on the posterior side and overhanging the interspaces, the orna- 

 rac-_-.„,_on GOFiSisting of oblique, mer'ially swollen nodules with 

 their extremi ' ' attenuated and Joine", prodiicing a spiral 

 effect; toward the center of the shell the frill becoming narrow- 

 er and sharper and the nodules correp"-'^-'''iri"'ly narrower and more 

 vertical in position; beyond the center the frill becoming wider 

 and separated from the smooth portion of the rib by a well defin- 

 es, b^it slight, groove; on "^b^ ^,en posterior ribs the frill ceas- 

 ing to be such, the line of nodules r lly assixming a central 

 position on the ribs, the nodizles then:selves becoming wider, 

 transversely swollen or globuJar -'>"'' almost or entirely diLrconnect- 

 ed, these posterior ribs lower and the interspaces wider; fine 



