172 BULLETIN 181, UNITE© STATES NlAnOiNAL MUSlEUM 



paler. The nucleus consists of about 2.5 well-rounded, smooth turns, 

 forming a small apex. The postnuclear whorls are well rounded with 

 a broad cord at the summit and an impressed area immediately ante- 

 rior to this. The postnuclear whorls are marked by rather strong, 

 retractively curved, axial riblets which are about as wide as the spaces 

 that separate them. Suture strongly impressed. Periphery well 

 rounded. Base openly umbilicated, well rounded and marked by the 

 continuation of the axial riblets which here are much weaker than on 

 the spire. They are again slightly stronger on the umbilical wall. 

 Aperture almost circular, slightly effuse at the junction of the basal 

 and outer lip; peristome thickened, expanded, and reflected and 

 marked by concentric lines of growth. The parietal wall has an obso- 

 lete lunate notch. Operculum typically cyrtotomid. 



The type, U.S.N.M. No. 515789, was collected by Dr. H. B. Baker at 

 Hacienda Cuatotolapam, Veracruz, Mexico. It has 5.4 whorls and 

 measures : Height, 17.0 mm. ; greater diameter, 23.0 mm. ; lesser diam- 

 eter, 16.8 mm. Height of aperture, 10.0 mm. ; diameter, 11.0 mm. 



U.S.N.M. No. 515790 contains a paratype from the same source. 

 U.S.N.M. No. 25011 contains 2 specimens merely labeled "Mexico," 

 which are referable here. 



This species can be differentiated from the other forms having a 

 subsutural thread by the obsolete notch on the parietal wall. 



CYRTOTOMA PALMERI, new species 



Plate 22, Figitees 1-3 



Shell depressed-helicoid ; the type is soiled white, having lost its 

 periostracum. Nuclear whorls about 2, well rounded, smooth, forming 

 a moderately small elevated apex. The postnuclear whorls are in- 

 flated, strongly rounded, and marked by retractively slanting axial 

 riblets, which are about as wide as the spaces that separate them. 

 These riblets gain in strength as the whorls increase in size. Suture 

 strongly impressed. The last whorl solute for about one-tenth of a 

 turn except the auricle at the posterior angle, which is adnate to the 

 preceding whorl. Behind this there is a deep broad open space in the 

 suture. Periphery well rounded. Base broadly openly umbilicated, 

 marked b}^ the continuation of the ribs, which are here somewhat wavy. 

 The umbilicus is broad, and its wall is marked by axial ribs, but here 

 they are weaker than on the base. Aperture broadly oval, with the long 

 axis extending from the parietal wall to the junction of the basal and 

 outer lip. Peristome very moderately expanded and reflected, adnate 

 to the preceding turn at the posterior angle. There is a very profound 

 sinus, which begins as a narrow slit near the edge of the peristome 

 then widens into a circular opening at the posterior termination. The 

 edge of this bulges inward and is somewhat thickened. 



