present, 'beGOKLii^- more prominent anteriorlj? and oostoriorlj; and 

 striatir;-- the Inraile and eGciitclicon. 



■Divcncions .- Len^tli, So. 5 . ui. ; cl':., '^'".5 mm.; semi'Uam., 9 ■ 

 Hemarks.- £. hendersonli i ;■ a proliflo form and at the sane 

 tirae is very varialole, f-e ^ne end of the series ^oeiii{^ ^'lore con- 

 vex and. having higher "urJoones, a steeper posterior slope, r.ir'"e ' 

 excavates '.n and a : liinule and escutcheon ^" 



the other. Such anti"oodal . te distinct, hnt are con- 



nected bj/ int ' '. " . ^'he nuj.iber of zihs is another uustahle 



feature, hnt is nc ' related v/ith the others, either enii pro-r. 



dMot havijT"'- ypi ativel/ 'f*!^''^ or nr'''T'-TO'-'f -'^ii-.s. The avera.p-e nnnii-\r.r 

 of rios is sixteen to ei"-iiteen. ./hen the interspaces are v/ide, "i; 

 a sequel of the re'^uction in the nunher of rihs, one or two of the 



iricrenentals in , :.nterspaces near th- " •"■''-in —^ oe 



emphasized. The rihs are very rarely as closely aopressed as is 

 shovm in Dall's figui^e. 



xhis species is characterized h; '^-'ther mtmerous ribs 



and the relatively ^ide poster! -r area over which the ribs are 

 lov/er and sharper. The form mentioned in the original descri o- 

 tion, 0_. ball iota Dall (l), from the -arapa silex be'^^s, has less 



(1). loc. cit., p. IPO.^., pi. 55, fig. ??:, 190?. 



numerous, occasionally ventral striate'"'., ribs that are atteni'iat- 

 ed closer to the dorsal margin. The Oak Grove 0. glyptocyia 



