BULIMULUS. xxiii 



the mesocone large, ectocone well developed. This type is continued 

 in the marginal teeth (pi. 57, fig. 63, B. limnoides, after Binney ; 

 fig. 64, B. dealbatus mooreanus). Distribution, from the southern 

 United States to northern Patagonia. 



The genus Bulimulus is more widely distributed than any other 

 group of the family. It is also the least specialized; the genera pre- 

 ceding being variously specialized in shell characters, those following 

 chiefly in characters of the teeth and jaws. It is likely that the com- 

 mon ancestors of all Bulimulidde were similar to Bulimulus both in 

 internal structure and shells. 



The multitude of subgeneric and sectional names which have been 

 proposed for minor groups of Bulimuli fall into three main divisions. 



I. Apical whorls smooth (p. xxiii.). 



II. Apical whorls irregularly wrinkled subvertically, or with the 

 wrinkles waved, dislocated, or broken into a thimble-pitted 

 reticulation (p. xxvi.). 

 III. Apical whorls with regular, straight, vertical riblets (p. xxxii.). 



DIVISION 1. Bui imuli with smooth apical whorls. 



The shell varies from obesely ovate to slender and column-shaped, 

 or rarely Heliciform, and from umbilicate to imperforate. It is 

 usually calcareous and opaque. The apical whorls are smooth and 

 glossy, without sculpture of any kind. Aperture ovate or angular, 

 the outer lip usually thin and simple, rarely expanded. Columella 

 foldless, dilated above. 



A group of plain-colored or whitish species characteristic of the 

 Pacific slope and Andean highland, from Ecuador to Chili ; with a 

 few thinner, corneous or brownish forms, referred here with some 

 doubt, in Bolivia and Argentina. 



The species have in common a small, smooth, often teat-like 

 nepionic shell. The subsequent growth is widely divergent in var- 

 ious forms, and hence a large number of " sections " have been 

 established, based upon the contour assumed by the adult shell 

 natural groups, but of only minor systematic value. 



Section Platybostryx Pilsbry, 1896. 



Depressed, wider than high, acutely keeled at the periphery and 

 around the broad, crater-shaped umbilicus. 

 B. eremothauma Pils., x, 129. Chili. 

 Helix reentsii Phil., preoc. 



