PUNCTUM. 7 



JICKELI, Fauna der Land- und Susswasser Moll. N.-O. Afrika's, in 

 Verb. K. Leopoldinisch-Carolinisch Deutschen Akad. der Naturfor- 

 scher, xxxvii, p. 54, t. 1, f. 4. 



Shell minute, thin, subdiscoidal but with convex spire, openly 

 umbilicated ; unicolored ; whorls about 4, convex, the apical 1 

 smooth, rather distinctly demarked from the following whorls, which 

 have oblique striae or irregular riblets and excessively fine spiral 

 stride ; the last whorl cylindrical, not descending in front. Aperture 

 lunate, rounded; lip simple, thin. Type P. pygmcKumvar. minutis- 

 simum, pi. 1, figs. 11, 12, 13. 



Jaw arcuate or horse-shoe shaped, composed of numerous (13-19) 

 separate rhomboidal plates, more or less overlapping, the outer 

 imbricating over the inner plates ; the median two or three plates 

 slightly separated, not overlapping. 



The individual plates are composed of vertical chitinous fibers 

 forming a fringe at the edges (fig. 6, 7, P. pygmceum) ; the plates are 

 bound together by a thin transparent membrane. The number of 

 plates varies somewhat, P. pygmceum (fig. 6) having 19 (Scliako) ; 

 P. pygmceum var. minutissimum having 16 (Morse'); P. conspectum 

 (fig. 9) having 14 to 16, P. cryophilum (fig. 5) having 13 plates. 



Radula rather long and narrow^ teeth rather separated, not in 

 the least overlapping. Central tooth tricuspid, the mesocone longest, 

 but not as long at the narrow basal-plate, side cusps small. Lateral 

 teeth having wider rhombic basal-plates and bicuspid, the mesocone 

 having a longer cusp. Marginal teeth not differentiated in any way 

 from the laterals, but becoming lower with shorter cusps (pi. 1, fig. 

 8, conspectum.) 



The number of transverse rows of teeth is 75 in P. conspectum, the 

 formula 17-1-17 (Pilsbry) ; in P. pygmwum there are 114 rows of 

 19-1-19 teeth (Schako) ; in P. pygmceum var. minutissimum, Morse 

 counted 54 rows of 13-1-13 teeth ; in P. cryophila there are 75 rows 

 of 16-1-17 teeth, according to Jickeli. Each transverse row bends 

 forward in the middle, as shown in the line above fig. 8, represent- 

 ing the curve of a half row. 



Distribution : North America, Europe, northern Asia and north- 

 eastern Africa. 



This genus differs from the other Patuloid Helices in having the 

 jaw composed of broad rhombic plates which are not in the least 

 soldered together, and in the peculiar form of the bicuspid lateral 

 teeth. It is evidently a type of vast antiquity, and probably has 





