64 [March, 



gradually "widening downwards to nbont the middle, from which point it again 

 very graduallj' contracts towards tlie narrowly ronnded front ; ovitcr lip thin ; 

 columella having a single small oblicjue fold, outside of which there is a small 

 umbilical groove. Length .25 inch, breadth .10 inch; apical angle regular, 

 divergence 57. 



Locality and position. Crow Creek near Black hills. No. 4 of the series. 



AvALANA SUBGLOBOSA. Shell globose or subovate ; spire very short, slopes 

 rounded ; volutions four, increasing rapidly from the ajjcx, last one veiy large 

 and ventricose ; surface ornamented by about thirty punctate stria?, half as wide 

 as the elevations between on the upper part of the volutions, but much more 

 closely croAvded on the lower part of the last turn ; suture linear, distinct ; 

 aperture semilunar, widest below, contracted and terminating in a smoothly 

 rounded angle above ; outer lip smooth within, faintly sinuate below and having 

 a thick strong peristome without ; inner lip thick and raised into a single promi- 

 nent tranverse tooth below. Length .39 inch, breadth .37 inch ; length of aperture 

 .21 inch, breadth .11 inch. 



Locality and position . Moreau trading post. No. 5 of the series. 



Natica ? AJiniGCA. Shell oblicjuely suboval, or oblong ; spire depressed-conical; 

 volutions about four, convex, increasing somcAvhat rapidly from the apex, last 

 one ventricose ; surface marked by fine lines of growth and stronger parallel 

 wrinkles, crossed by strong irregular revolving stri;\? ; suture distinctly impressed, 

 aperture obliquely ovate, angular above, rounded below ; lips thin, ajiparently 

 disunited above and abrujitly deflected outward on the inner side below the 

 small or rudimentary umbilicus. Length .50 inch, breadth .42 inch ; length of 

 aperture .34 inch, breadth of do. .24 inch ; apical angle convex, divergence 81. 



Locality and ^josilion. Same as last. 



Natica occidentalis. Shell obliquely-oval or ovate ; spire elevated ; volutions 

 about five, convex ; surface marked with fine lines of growth, andfaint or nearly 

 obsolete, minutely tiexuous revolving lines; suture distinctly impressed ; aperture 

 ovate, straight on the inside and broadly rounded without ; outer lip thin ; inner 

 lip not thickened, partly deflected over the edge of the small oblique umbilicus. 

 Length about .97 inch, breadth .70 inch ; length of aperture .56 inch, breadth 

 .33 inch ; apical angle convex, divergence 70. 



Locality and position. Same as preceding. 



Natica Moreauensis. Shell obliciuely-ovate ; spire somewhat depressed; 

 volutions three and a half to four, convex, last one large and ventricose ; surface 

 marked )jy fine lines of growth, crossed by A'ery fine, nearl;y obsolete, minutely 

 flexuous revolving lines ; suture distinctly impressed or sub-channeled ; aperture 

 ovate ; outer lip thin; inner lip not thickened and deflected partly over the small 

 umbilicus. Length about .90 inch, breadth .70 inch ; length of aperture .54 

 inch, lireadth .36 inch ; apical angle slightly convex, divergence 90. 



Locality andposition. Same as preceding. 



TuBBO Nebrascensis. Shell turbinate, length and breadth about equal ; spire 

 broadly conical ; volutions about five, ronnded, gradually increasing from the 

 apex ; surface ornamented by fine revolving stria', crossed by delicate lines of 

 growth, becoming distinct oblique wrinkles along the suture and round the um- 

 bilicus, the whole presenting an elegant cancellated appearance under a lense ; 

 suture distinctly impressed ; aperture round ; umbilicus moderate, round. 

 Length .25 inch, breadth .26 inch; diameter of aperture .12 inch; apical angle 

 somewhat convex, divergence 53. 



Locality and position. Yellow Stone river, one hundred and fifty miles from 

 mouth. No. 4 of series. 



Turbo tenuilineatus. Shell oblong or suboval, oblique, thin ; spire some- 

 what elevated, acute at tlie apex ; volutions about five, rounded, increasing 

 rapidly from tlie apex; last one ventricose, extended in front ; surface marked 



