Dentition of Pulmonate Mollusks. 95 
Plagioptycha. 
Jaw arcuate, ends slightly acuminated, blunt; no anterior ribs ; 
/adecided median projection to the cutting edge:—P. loxodon, 
| Pir., Aldersiana, Pir,, monodonta, Pfr., diaphana, Lam., macro- 
' giossu, Pir. In P. Duclosiana, Keér., however, there is a decided 
median, stout rib, denticulating either margin. Thus the pres- 
ence or absence of ribs on the jaw cannot be considered a generic 
character in Plagioptycha. 
The character of the lingual dentition in the species examined 
agrees. 
Plagioptycha locodon, Fer. San Domingo. Dr. W. Newcomb. 
i Lingual membrane (PI. V, fig. C) long and narrow. Centrals having a 
j long, narrow base of attachment, with expanded lower angles and lines of 
- reinforcement within them; reflected portion small, with a single stout cusp 
) and cutting point ; laterals like centrals, but asymmetrical ; outer laterals 
| with outer cusp and cutting point; the inner cutting point becomes bifid as 
the teeth pass into marginals, which become low and wide, with two broad, 
bluntly rounded, usually bluntly bifid cutting points. 
Plagioptycha Albersiana, Pir. 
Jaw as above. 
| Lingual membrane like last. (Pl. V, fig. D.) 
Plagioptycha monodonta, Pfr. San Domingo. Dr. Newcomb. 
| Jaw as above. 
Lingual membrane (Pl. V, fig. E) like that of P. fowodon. 
Plagioptycha Duclosiana, Fer. Exuma, Bahamas. Dr. J. J. 
| Brown. 
Jaw as described above. 
Lingual membrane \PI. V, fig. F) with about 30-1-30 teeth. The figure 
shows the gradual changes in the teeth, the seventh being the last lateral. 
_ The side bulgings in the cutting points of central and first laterals are shown 
_by using a different focus in the microscope than that used in drawing the 
figures of the other species. It represents the side cutting point. 
) 
! 
{ 
Plagioptycha diaphana, Lam. Porto Rico. Dr. Cleve. 
Jaw as above. 
Lingual membrane (Pl. V, fig. G) as in lovodon. 
Plagioptycha macroglossa, Pfr. 
Jaw as above. 
Lingual dentition (Pl. V, fig. H) as in loxodon. 
