178 BULLETEN" 181, UNITED STATEiS NlATIOiNlAiL MUSETJM 



The specimen described and figured, U.S.N.M. No. 162825, is one 

 of two collected at San Carlos, Costa Rica. It has 5.5 whorls and 

 measures: Height, 25.2 mm.; greater diameter, 33 mm.; lesser di- 

 ameter, 25 mm. 



This species resembles most nearly B. UTiderwoodi (Da Costa), 

 from which its small size readily distinguishes it. 



CALACYCLOTUS, new genus 



Amphicyclotine shells of helicoid outline, without color bands, with 

 the axial sculpture reduced to incremental lines, and the spiral sculp- 

 ture absent or microscopic. Base widely umbilicated. Aperture de- 

 cidedly oblique; outer lip of peristome somewhat expanded and re- 

 flected at the outer lip, the parietal and columellar peristome forming 

 a sigmoid edge. 



Type: Calacyclotus olssoni (Pilsbry). 



Distribution: Panama and Colombia. 



KEY TO THE SPECIES OF CALACYCLOTUS 



Greater diameter more than 50 mm olssoni 



Greater diameter less than 42 mm atratensis 



CALACYCLOTUS OLSSONI (Pilsbry) 



Plate 23, Figures 13-15 



1926. AmphicTjclotus olssoni Pilsbky, Proc. Acad. Nat. Sci. Philadelphia, vol. 

 78, pp. 65-66, pi. 9, figs. 1, la. 



Shell very large, uniformly chestnut-brown, with the tip red and 

 the inside of the aperture bluish white. Nuclear whorls about 2, 

 well rounded, smooth, forming an inconspicuous apex. Postnuclear 

 whorls well rounded, marked by slender, retractively curved incre- 

 mental lines only. Suture well impressed. Periphery strongly 

 rounded. Base well rounded, openly umbilicated, with the umbilicus 

 about equal to one-fourth of the diameter of the shell, marked by 

 the continuation of the incremental lines, which pass over the um- 

 bilical wall, where they became somewhat stronger. Aperture de- 

 cidedly oblique, broadly pear-shaped, protracted into an angle at the 

 posterior angle of the aperture. Peristome expanded on the outer 

 and right portion of the basal lip, thickened on the inner lip. Parie- 

 tal wall covered with a moderately thick callus, which forms an 

 obtuse angle at its junction with the columella. Pilsbry says of 

 the operculum of this species : "The operculum is flat, dull brownish, 

 of about 12 whorls, the outer four subequal, diminishing slightly 

 to the last, smoothish. Interior face with a small central mucro 



