168 BULnETTN 181, UNITED STATES NlAnPEONlAJL MUSEUM 



covering the upper surface of the whorls, except for a white band at 

 the summit and at the suture. The nucleus consists of almost 2 turns, 

 which are smooth. The postnuclear whorls are marked by spiral 

 threads, of which 7 are present on the anterior half of the whorls; 

 on the posterior half there are indications of more, but they gradu- 

 ally evanesce toward the summit. On the last half of the last whorl 

 they become completely obsolete. In addition to this there are micro- 

 scopic spiral lirations. The incremental lines are decidedly oblique 

 and moderately strong, and rather irregular on the last turn. Suture 

 rendered inconspicuous by the appressed summit of the whorls. 

 Periphery well rounded. Base inflated, strongly rounded, and 

 marked by 13 spiral threads between the periphery and the edge of 

 the umbilicus. These are decidedly stronger than those on spire and 

 continue to the peristo,me. The base is broadly open and umbilicated 

 and the umbilical wall is marked by incremental lines. Aperture 

 broadly pear shaped, decidedly protracted at the posterior angle; peri- 

 stome slightly reflected, simple. Operculum with central nucleus, 

 slightly concave ; the outer edge of the whorls is marked by lacinations, 

 which are striated. 



The specimen described and figured, U.S.N.M. No. 307420, comes 

 from the Island of Tumaco, Colombia. It has 6.4 whorls and meas- 

 ures: Height, 27 mm,; greater diameter, 45,8 mm,; lesser diameter, 

 34,5 mm. 



The huge size of this species readily distinguishes it from the 

 other members that have the spiral cords obsolete on the last turn. 



CALAPEROSTOMA ORBIGNYI (Ancey) 



1892. Cyclophorus orhignyi Ancey, Journ. Conch., vol, 7, p. 94. 

 1897. Amphicyclotus orbignyi Kobelt and Mollendoeff, Nachrb, deutschen 

 malak. Ges., vol. 29, p. 139. 



Shell depressed-discoid, broadly openly umbilicated, solid, soiled 

 white below a deciduous fulvous periostracum, reddish on the early 

 turns, rough or shining. Spire slightly elevated, the apex small, 

 inconspicuous. Whorls 5, increasing regularly and rapidly in size, 

 convex. Suture deep, the first three whorls smooth, the following 

 ones acutely lirate, the threads being prominent and regular and well 

 elevated at the periphery and on the base* the upper vary and they 

 increase by intercalation. The last whorl is cylindric, and slightly 

 descending near the aperture. The umbilical wall is smooth or 

 slightly lirate. The umbilicus is one-fourth of the diameter of the 

 shell or a little larger. Aperture oblique, circular, angulated above ; 

 peristome continuous, simple, appressed to the preceding turn. Oper- 

 culum corneous, thin, concave externally with the whorls closely 

 spaced. 



