Dentition of Pulmonale Mollusks. 95 



Plagioptyclia. 



Jaw arcuate, ends slightly acuminated, blunt; no anterior ribs ; 

 a decided median projection to tiie cutting edge:— P. loxodon, 

 Pfr., Albersiana, Pfr,, monodonta, Pfr., diaphana, Lam., macro- 

 glossa, Fir. In P. Duclosiana, Fer. , 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 Ptagioptycha. 



The character of the lingual dentition in the species examined 

 agrees. 



Ptagioptycha loxodon, Fer. San Domingo. Dr. W. Xewcomb. 



Lingual membrane (PI. Y, fig. C) long and narrow. Centrals having a 

 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 as} r mmetrical ; 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. 



Ptagioptyclia Albersiana, Pfr. 



Jaw as above. 



Lingual membrane like last. (PI. Y, fig. D. ) 



Ptagioptyclia monodonta, Pfr. San Domingo. Dr. Xewcomb. 



Jaw as above. 



Lingual membrane (PI. Y, fig. E) like that of P . loxodon. 



PlagiojJtycha Duclosiana, Fer. Exuma, Bahamas. Dr. J. J. 

 Brown. 



Jaw as described above. 



Lingual membrane V P1. Y, 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. 



Ptagioptycha diaphana, Lam. Porto Rico. Dr. Cleve. 



Jaw as above. 



Lingual membrane (PI. Y, fig. G; as in loxodon. 



Ptagioptycha macroglossa, Pfr. 



Jaw as above. 



Lingual dentition (PL Y, fis:. H) as in loxodon. 



