Occasional Papers of the Museum of Zoology 5 



Both folds are more strongly indicated in the aperture than 

 in the case of the United States species, and they reach their 

 greatest development correspondingly earlier in the course of 

 the turn about the columella. 



Carychiuni exiguum var. ? 



The six shells figured under this name were collected neaf 

 Harbert, Berrien County, Michigan, on the moist ground and 

 debris of a wooded ravine between sand dunes, near the Lake 

 Michigan beach. In size and smoothness they closely resem- 

 ble C. nannodcs, and the internal lamellae in shape and size 

 seem to bear out the similarity. They were submitted to Dr. 

 Clapp, who writes that he thinks the "aperture is proportion- 

 ately narrower" in nannodes than in the Michigan shells, and 

 that the latter should be considered a "dwarfed, narrow form 

 of exiguum." The difference in aperture is not evident upon 

 comparison of the six shells with cotypes of nannodes (loaned 

 by Dr. Walker) and the flatness of the body whorl is not like 

 the obeseness of exiguum, though this may be one evidence 

 of dwarfedness. It seems fairly possible that both nannodes 

 and the Michigan shells are depauperate forms, arising from 

 the same stock or converging from different stocks, the south- 

 ern form having become stabilized, while the northern one 

 still appears only sporadically. Nannodes was found in num- 

 bers in company with "a coarsely ribbed exile," while the 

 exiguum var. ? was collected with exiguum, and a few exile 

 and exile canadcnse, seeming to make the probability greater 

 that the Michigan shells are depauperate individuals of the 

 common form {exiguum) rather than an apparently distinct 

 race like nannodes. 



The lamellae are almost identical in the two forms, as may 



