^4 PLEURODONTE. 



they replace Labyrinthus of the lower regions of northern South 

 America. The shells differ from Labyrinthus in the more or less 

 transversely dilated contour, the swollen base of the latter portion 

 of the body-whorl, and the less developed aperture-teeth. In a few 

 species (cenigma, vexans) the teeth are strongly developed ; but these 

 are to be regarded as an independent line of evolution from typical 

 Isomeria, rather than as an intermediate or ancestral form between 

 Isomeria and Labyrinthus. 



Species. 



P. oreas Koch, v, 136. 



procera Pfr. 

 P. faunus Phil., v, 1 37. 



v. ritchieana Pils., v, 138. 

 P. subelliptica Mouss., v, 139. 

 P. continua Pfr., v, 137. 

 P. aloagana Jouss., v, 139. 

 P. peritropis Pils., v, 140. 

 P. fordiana Pils., v, 141. 

 P. calomorpha Jonas, v, 142. 

 P. sequatoriana Hid., v, 142. 

 P. scalena v. Mart., v. 143. 

 P. meobambensis Pfr., v, 144. 

 P. atrata Pfr., v, 144. 

 P. mauritii Jouss., v, 145. 



atrata Rv. not Pfr. 

 P. cymatodes Pfr., v, 146. 

 P. parietidentata Mill., v, 147. 

 P. kohlbergi Mill., v, 148. 

 P. martinii Bern., v, 149. 



morula Hid. 



P. granulatissima Mill., v, 148. 

 P. gealei E. A. Sm., v, 149. 

 P. stoltzmanni Lub., v, 150. 

 P. sequatoria Pfr., v, 150. 

 P. equestrata Moric., v, 151. 

 P. triodonta d'Orb., v, 152. 

 P. juno Pfr., v, 152. 

 P. neogranadensis Pfr., v, 153. 

 P. hartwegi Pfr., v, 153. 



loxensis Mill. 



P. basidens Mouss., v, 154. 

 P. bituberculata Pfr., v, 154. 



bourcieri Rv. not Pfr. 



v. tridentula Mill., v, 155. 



v. latideutata Mill., v, 156. 

 P. bourcieri Pfr., v, 156. 



bituberculata Rv. not Pfr. 

 P. subcastanea Pfr., v, 157. 



globosa Brod. not Sowb. 

 P. senigma Dohrn, v, 158. 

 P. vexans Dohrn, v, 158. 



Section Labyrinthus Beck, 1837. 



Labyrinthus BECK, Index Moll., p. 33, type L. otis=labyrinthus 

 Dh. PILSBRY, Manual of Conch. (2), v, p. 159. MARTENS, Biol. 

 Centr. Amer., Land Moll., p. 175. Lyrostoma SWAINS., Malacol. 

 p. 329, type L. labyrintha. Lyriostoma SWAINS., I. c., footnote 

 <1840). 



Shell umbilicate, depressed, carinated, microscopically granulated, 

 not transversely dilated. Whorls less than 6, the last descending in 



