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JOURNAL OF CONCHOLOGY, VOI,. I4, NO. 5, JANUARY, I914. 



seen four species — two from East i^frica, one from Oregon, and one 

 from Tasmania. These also have bicuspid centrals and comb-like 

 marginals, but the laterals are set on large quadrate bases, and the 

 oblique tops are broader and larger — in all this resembling the larger 

 species of Planorhis, which also we may distinguish as Type (B). 

 The jaw is of the usual type in Limna'a, with two accessory plates. 

 A. kiamathetisis from Oregon belongs here, but its unicuspid central 

 brings it still nearer to Liiiincea. If, then, we divide Puinorbis into 

 two groups, the smaller species almost exactly agree with this Southern 

 section, while the larger differ from it by having a shorter radula with 

 the front end rounded, and by having the laterals on a broader and 

 more solid basis. Among the smaller species I count PI. albiis, PL 

 con tortus, and even PI. marginaius ; to the larger belong PL corneus 

 and PL. trivolvis. 



Merging Segmentina in Planorbis th 

 Type (A) like Type (A) of AncyLus- 



Planorbis albus fMiill.). 



P. anderssoni Ancey. 



P. ariniger Say. 



P. austraLicus Sm. 



P. brazieri Allison. 



P. carlnatiis Miill. 



P. cotifortus L. 



P. costuLaLii s Krauss. 



P. crawfordi M. & P. 



P. cnltratus L. 



P. dilatatus Gld. 



P. exaciitiis Say. 



P. haldefiiani C. B. Ads. 



P. japotiiais Mtg. 



P. leucocJiiLus M. & P. 

 -Thirty species, mostly small. Distr 



e list stands thus :^ 



P. liinopliilns Westl. 

 P. Lineaius ^^^alker. 

 P. vwntroiizieri Gass. 

 P. nautileus L. 

 P. nitidus Miill. 

 P. opercidaris Gld. 

 P. parvus Say. 

 P. planodiscus M. iSc 1 

 P. poLaris Schm. 

 P. saigonetisis Cr. & ] 

 P. soudanicus \\\\.?>. 

 P. spirorbis \l\\\\. 

 P. unibiHcatus Miill. 

 P. vortex L. 

 P. wLieatleyi Lea. 

 ibution s:eneral. 



Type (B), like Liimma, but bicuspid centrals: — 



Planorbis bicarinatus Say. 

 P. biitneyi Tryon. 

 P: budouxianus Bgt. 

 P. canipanulatus Say. 

 P. corneus L. 

 P. coromandelicus Beck. 

 P. decipiens C. B. Ads. 

 P. declivis Sby. 

 P. dufouri Graells, 



P. exustus Desh. 

 P. fieldii Tryon. 

 P. guade!o7tpensis Sby. 

 P. oregonensis. 

 P. peregrinus Orb. 

 P. pfeifferi Krss. 

 P. straniineus Dkr. 

 P. trivolvis Sa)'. 



