426 



irregularly crenulate; the last whorl rapidly increasing in size, being equal in 

 width to the other two whorls together; the lamella only slightly elevated 

 and not extending over the spiral suture; nucleus strongly eccentric. 



Length Width Aperture 







(Inner 



diameter) 





14.5 



8.5 



4.0 



mm. 



Type, incomplete 



13.0 



7.0 



3.5 





Paratype, complete 



13.5 



7.5 



4.0 





Paratype, incomplete 



15.0 



8.5 



4.0 





Paratype, complete 



15.5 



9.5 



4.5 





Paratype, incomplete 



12.5 



7.5 



3.5 





Paratype, complete 



Holotype. — Univ. of Michigan no. 49190, from Chichen Itza, Yucatan,' 

 collected by F. M. Gaige, January, 1930. 



Paraty pes. —M.C. Z. no. 79390, data as above; and M. C. Z. no. 79783, 

 from Chichen Itza, collected by J. Bequaert, June, 1929. 



Remarks. — This species is allied to Choanopoma chiapasense 

 Crosse and Fischer (1877, Jour, de Conchyl. 15, p. 362; 1890, 

 Miss. Set. Mexique, Moll. Terr. Fluv. 2, p. 182, pi. 41, fig. 8-8a), 

 from the State of Chiapas, Mexico. It differs by being much 

 smaller, the largest complete specimen measuring 15.5 mm., 

 while incomplete C. chiapasense, of 4^ whorls, measures 17.5 to 

 18 mm. The characters of the operculum appear to be quite 

 different: that of C. gaigei has a strongly eccentric nucleus and 

 rapidly broadening whorls; whereas in C. chiapasense the nucleus 

 is described as 'slightly eccentric, almost central/ and the spiral 

 s figured as composed of very gradually enlarged whorls. The 

 sculpture of C. gaigei appears to be much stronger than that of 

 C. chiapasense. An interesting feature of the new species, not 

 found in C. chiapasense, is the tendency to retain all of the 

 apical whorls to the adult stage. 



