PLEURODONTE. 95 



front, constricted behind the peristome. Aperture transverse, sub- 

 horizontal, obstructed by three primary folds or teeth, one long 

 parietal fold, one tooth on the outer, another on the inner portion of 

 the basal lip ; peristome expanded or reflexed in every part, con- 

 tinuous across the parietal wall. Type P. labyrinthus, pi. 25, figs. 4, 

 5. (See also pi. 22, figs. 7, 8, P. sieversi). 



Soft parts unknown. Jaw slightly striated (Morch, Journ. de 

 Conch. 1865, p. 381), with a slight median projection. Teeth all 

 uni-cuspid (Semper, Reisen, p. 105) as in the Cuban Caracolus. 

 (PI. 26, fig. 9, P. plicata Born, after Semper). 



This group is characteristic of northern South America, extend- 

 ing from the Amazon River and its western tributaries in eastern 

 Peru, northward in Central America to Costa Rica. It inhabits less 

 elevated regions than the allied group Isomeria. Its complicated 

 aperture-armature has doubtless been evolved for protection against 

 predaceous insects (c/. Man. of Conch, v, p. 159; Biol. Centr. Amer. 

 Moll., p. 175 ; Pop. Sc. Monthly, 1892, p. 191). 



Labyrinthus agrees with the restricted section Caracolus in teeth 

 and jaw, as well as in the general features of the shell. It stands in 

 about the same relation to Caracolus that Triodopsis and the auri- 

 culate Polygyras hold toward the toothless Mesodons. There seems 

 no sufficient reason for considering Labyrinthus a distinct genus, as 

 von Martens has done. 



Species. 



P. labyrinthus (Chem.) Dli. v, P. leucodon Pfr., v, 167. 



subplanata Petit. [161. P. sieversi v. Mart., viii, 263. . 



v. erecta Mouss., v, 162. P. quadridentata Brod., v, 168. 



v. sipunculata Forbes, v, 162. P. tamsiana Dkr., v, 169. 



annulifera Pfr. P. tarapotonensis Moric., v, 170. 



P. plicata Born, v, 163. P. bifurcata Desh., v, 170. 



hydiana Lea. P. furcillata Hupe, v, 171. 



hydeanus v. Mart. P. raimondii Phil., v, 172. 



P. uncigera Petit, v, 164. P. yatesi Pfr., v, 173. 



conoidea Anc., viii, 264. P. ellipsostoma Pfr., v, 173. 



anopla Anc., viii, 264. P. leprieurii Petit, v, 174. 



v. creveauxiana Anc., viii, 264. auriculina Petit. 



P. triplicata v. Mart., v, 165. P. dunkeri Pfr., v, 174. 



cesopus Ang. P. isodon Pfr., v, 175. 



