66 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



Chemn., from Martinique, has a strongly developed peristome, 

 bearing two or more teeth or denticles on the basal and two on the 

 outer margin, with a very strong, raised lamina on the parietal 

 callus, the aperture being still further reduced by constriction 

 behind the peristome. P. nigrescens, Wood, an inhabitant of the 

 island of Dominique, bears a strong, obliquely entering lamella on 

 the parietal wall, a short, strong fold on the columellar margin, and 

 a longer, entering lamella on the basal margin of the peristome, with 

 a corresponding scrobiculation. 



P. auridens, Rang, the only species of the section G-onostomopsis, 

 Pilsbry, from Martinique, and its variety oligotricha, Anc, is only 

 provided with a short, raised lamella on the outer margin of the 

 peristome. The section Caracolus, Montf., occurring in Cuba, 

 Haiti, and Porto Rico, is composed of large species with ample 

 aperture devoid of teeth or lamellse. 



The section Isomeria, Alb., confined to Ecuador, Colombia, and 

 Peru, has most of its species furnished with one or more small 

 denticles on the peristome, while a short parietal fold is also found 

 in some species. P. suhcastanea, Pfr., is^ an exception, having 

 a strong, entering lamella on the outer part of the basal margin 

 with a corresponding deep scrobiculation 



The section Ambages, Gude, consists of only two species 

 from New Grenada, P. vexans, Dohrn, and P. cenigma, Dohrn, 

 the latter twice the size of the former, but both having the 

 armature on the same plan. The aperture is ear-shaj)ed and 

 considerably narrowed by its lamellas ; the basal margin is 

 sinuous, strongly callous, and reflected, bent upward in the 

 middle, forming an obtuse, squarish process ; the upper and outer 

 margins broadly expanded, arcuate, and bearing a short, entering 

 fold in a line with the peripheral angulation, and below this a strong, 

 raised, entering lamella, .with a corresponding deep scrobiculation 

 behind the peristome ; the parietal callus has the margin sinuous, 

 raised, continuous with the peristome, and gives ofi about the middle 

 a very strong, raised, flexuous, obliquely entering lamella. 



The section Labyrinthus, Beck, stands out from the other 

 members of the group on account of the considerable constriction of 

 the aperture in many of the species. It is characteristic of northern 

 South America, extending northward in Central America as far as 

 Costa Rica. They are all more or less flattened shells with narrow 

 aperture. P. labyrinthus, Chemn., from Panama, has a strongly raised 

 parietal callus continuous with the peristome and giving ofi a strong, 

 median, sinuous, obliquely entering lamina, which almost meets a 

 strong, high, triangular, entering lamina on the outer end of the basal 

 lip, which bears a second, smaller lamina nearer the columella, with 

 a deep sinus between them and corresponding deep pits or scrobicu- 

 lations behind the peristome. P. bogotensis, Pfr., has the parietal 

 callus and lamina similar to those found in P. cenigma and vexans, 



