THE CYCLOPHORID LAND MOLLXJStKS OF AMEKIOA 179 



with a low encircling ridge forming a ring of about 5 mm. diameter. 

 The dull scar of attachment is broadly oval, eccentric, its edge notched 

 where it passes the mucro." 



The specimen described and figured, U.S.N.M. No. 341767, was 

 collected by A. E. Heighway at Acandi, a small settlement in the 

 Gulf of Atrato, on the boundary between Panama and Colombia. 

 It has 6.1 whorls and measures : Height, 33 mm. ; greater diameter, 

 53.8 mm. ; lesser diameter, 39 mm. 



The large size readily distinguishes this species from C. atratensis. 



CALACYCLOTUS ATRATENSIS, new species 



Plate 23, Figures 10-12 



Shell helicoid, covered with a chestnut-brown periostracum ; the 

 early whorls reddish; interior of the aperture yellowish white. Nu- 

 clear whorls about 2, well rounded, smooth, forming a smaU apex. 

 Postnuclear whorls marked by rather irregular, retractively slant- 

 ing incremental lines. Suture moderately impressed. Periphery 

 well rounded. Base openly umbilicated, the umbilicus being about 

 one-fourth the diameter of the shell, marked by the continuation 

 of the incremental lines, which here assume almost the strength of 

 riblets; these pass also over the umbilical wall. Aperture de- 

 cidedly oblique, almost circular, protracted into an auricle at the 

 posterior angle. Peristome somewhat expanded on the outer lip 

 and somewhat thickened on the inner, covering the parietal wall with 

 a thick callus. The edge of this callus on the parietal wall and 

 columella forms a decidedly ragged sigmoid curve. 



The type, U.S.N.M. No. 206291, was collected by A. E. Heighway 

 on the mountains near the mouth of the Atrato Kiver in Colombia. 

 It has 5.9 whorls and measures : Height, 25.2 mm. ; greater diameter, 

 41 mm. ; lesser diameter, 31 mm. 



The small size readily distinguishes this species from C. olssoni 

 (Pilsbry). 



MEXCYCLOTUS, new genus 



Small amphicyclotine shells of helicoid outline, marked by axial 

 hairlines only. Operculum corneous, concave, with more than 10 

 whorls, which have their outer edge upturned, free, or appressed to 

 the succeeding whorl. The turns of the lamella are obliquely striated. 



Type: Mexcyclotus lutescens (Pfeiffer). 



Distribution: Southwestern Mexico. 



The members of the genus recall Aperosfoma {Cyclohidalgoa) 

 translucidum (Sowerby), but that group has a calcareous operculum. 



