CRETACEOUS FOSSILS. 425 



rather straightened on the inner side and shghtly produced below ; volu- 

 tions crossed by numerous vertical folds or plica', which are very slightl}' 

 bent backwards in their course across the volution Surface of the sliell 

 unknown. 



The specimen from which the description is drawn is an internal cast, 

 and therefore the external characters cannot be given in detail. The species 

 is, however, so entirely distinct from any of the forms known from this 

 region, that there is no fear of its being confounded with any of them. 



Formation and locality. — In gray shales near the upper part of the P^ort 

 Pierre Group, on the Cheyenne River near Rapid Creek, Black Hills. 



APORRHAIDiE. 



Genus APORRHAIS Dillwyn. 

 APORRHAIS NEWBERRYI. 



Plate Vi, i\g. 4. 



Anchura ? neicberryi Meek, Rept. ou Capt. Macomb's Exp., p. 129, PI. 11, fig. 5. 



Shell small or of moderate size; spire elevated, composed of about four 

 subangular volutions, exclusive of the body whorl, as seen on the back of 

 the shell ; apical angle about 40^. Volutions marked by a distinct angula- 

 tion about one-third of their height above the suture line, and the body vol- 

 ution by a second smaller carination a short distance below the first; also 

 by fine revolving lines, which alternate in their degree of strength; three of 

 the stronger ones may be counted above the carination on the back of the 

 outer volution, with a narrow smooth space above the carina, one strong and 

 two smaller lines between the carinations, and five strong ones with finer 

 ones between on the lower side of the volution. Outer lip expanded and 

 extended in two long, slender, diverging digitations, corresponding to the 

 carination on the outer volution, the lower one directed slightl}' forward in 

 the direction of the coil of the shell ; margin of the lip bordered by a thick- 

 ened rounded rim ; anterior prolongation or canal not observed ; posterior 

 canal extended along the spire to the summit, where it is deflected and 

 extended bej^ond to an unknown length ; callus of lip coating the entire 

 spire and upper part of body volution, obscuring or concealing the revolv- 



