1916] Weaver: Tertiary Faunal Horizons 49 



all specimens have a much higher spire; twelve instead of nineteen longitudinal 

 ribs ; in the spacing and general character of the revolving threads and the presence 

 of a non-ornamented band just posterior to the siphonal fascicle at end of canal. 

 Each whorl of the spire is about twice as high as in the case of Strepsidura oregon- 

 ensis. 



It differs from S. calif 'arnica in the character of the finer ornamentation and 

 the longitudinal ribbing. 



Dimensions Altitude of shell 34 mm.; altitude of spire 12 mm.; maximum diam- 

 eter of shell 21 mm.; angle of spire 60. 



Occurrence At locality 256 (University of Washington Palaeontological Col- 

 lection) in railway cuts on the O.-W. R. R. & N. Co. one fourth mile northwest 

 of Lincoln Creek Station in Section 27, Township 15 North, Range 3 West. 



Horizon Lowermost Oligocene; Molopophorous lincolnensis Zone. 



STREPSIDURA LINCOLNENSIS n. sp. 

 Plate IV, Figures 62 and 63 



Description Shell of medium size, spire short and canal moderately elongate; 

 whorls six in number, the body whorl being exceptionally large; upper portion of 

 each whorl is angulated and surface above the angle is very slightly concave and 

 merges gradually into the surface below the angle of the whorl above; surface 

 sculptured by four square topped ribs above the angle with broad flat bottomed 

 interspaces of triple width within which are three to five revolving threads ; middle 

 portion of surface below angle has three well defined revolving ribs and the inter- 

 spaces are set with two or three minor ribs ; lower part of body whorl sculptured 

 with ten very prominent ribs with interspaces of double width each of which is 

 set with a single small revolving thread ; revolving ribs are crossed by fourteen 

 longitudinal ribs which are well defined on middle portion of whorl but somewhat 

 obscure on upper and lower portions. Aperture semi-elliptical; anterior end ex- 

 tended into a somewhat elongate slightly twisted canal ; outer lip thick ; inner lip 

 heavily callused with the callus extending over a portion of the ornamented sur- 

 face of shell but so thin that the ornamentation shows distinctly through; no plica- 

 tions are present on the inner lip or columela. 



Dimensions Altitude of shell 41 mm.; altitude of spire 10 mm.; maximum 

 diameter of shell 26 mm.; angle of spire 65. 



Occurrence At locality 256 (University of Washington Palaeontological Col- 

 lection) in railway cuts on the O.-W. R. R. & N. Co. one fourth mile northwest 

 of Lincoln Creek Station in Section 27, Township 15 North, Range 3 West. 



