NEOPETR^US. 163 



nearly vertical, the peristome subcontinuous, margins joined by a 

 thin, shining callus, outer margin well incurved and lengthy, effuse 

 toward the base ; columellar margin dilated, nearly concealing the 

 perforation ; columella obliquely twisted, sinuous. Alt. 47, greatest 

 diam. 17 mill.; aperture with peristome 24 mill. long. 14 wide (71/a- 

 bille). 



Lower California (Diguet). 



Bulimulus (Leptobyrsus} subspirifer MABILLE, Bull. Soc. Philo- 

 math. (8), vii, p. 67, 1895. 



Genus NEOPETR^EUS von Martens, 1885. 



Neopetrceus v. MART., Conchologische Mittheilungen, i, p. 194 



(1885). 



Bulimulidse with ovate or oblong, rather solid shells, rimate or 

 umbilicate, the lip generally expanded ; young shells carinated ; 

 nepionic sculpture of delicate vertical riblets, predominating over 

 the closer, finer and lower spiral striae of the intervals. Dentition 

 peculiar. Type N. millegranus v. Mart. 



Distribution, valley of the Maranon River and adjacent parts of 

 Peru. 



Illustrated on plates 29, 30, 31, 32, with some figures on pi. 25 

 and 33. 



Neopetrceus was originally proposed as a subgenus of Otostomus 

 (Drymseus), for three species differing notably from that genus 

 in dentition, the central teeth being unicuspid, laterals with ex- 

 tremely long, oblique cusps, formed by coalescence of ento- with 

 mesocoues, as shown by a nick or emargination in the end. The outer- 

 most marginal teeth retain the earlier tricuspid form in some species, 

 but in others seem all to have been transformed, and resemble the 

 laterals. 



No conchological features were mentioned by von Martens, distin- 

 guishing the group from other subgenera ; probably because in 

 general characters, some species have no definable differences from 

 Scntalus, others from Drymceus. 



In the sculpture of the nepionic whorls, however, I find a concho- 

 logical character which places the group upon a basis of practical 

 utility, enabling us to ascertain its limits, in most cases, without re- 

 ference to the soft parts, which are necessarily inaccessible in the vast 

 majority of specimens. The nepionic sculpture (pi. 33, fig. 49 ; pi. 31, 

 fig. 20) consists of delicate subvertical riblets, the intervals between 



