VII. 

 SYSTEMATIC ACCOUNT OF THE SUB- 

 FAMILIES, GENERA, AND SUBGENERA 

 RECENT AND FOSSIL 



PLANORBIDAE, together with the Physidae and Bulinidae, are 

 animals with spiral shells; the genitalia and the respiratory and 

 excretory organs are on the left side. The shell of Planorbidae is 

 typically sinistral in some groups (Helisoma) and pseudodextral or iiltra- 

 dextral in many groups. The shell is carried almost vertically in the typi- 

 cally sinistral groups but leans toward the left in other groups, principally 

 the smaller forms. In these groups the spire is beneath and the umbilicus 

 is above, these being respectively the right and left sides of the shell. The 

 central tooth of the radula is always bicuspid. In Physa it is multicuspid. 



The chief feature separating the Planorbidae from the other members 

 of the Limnophila is the presence of an accessory breathing organ, the 

 pseudobranch, which takes over the office of a gill when the animal is sub- 

 merged and can not obtain free air. The flattened, 'planorboid' shell is, of 

 course, another distinctive feature of the family. 



The groui)s of genera related to Bulinm and Physopsis have in the past 

 been included in the family Planorbidae because of the similarity of the 

 radulae and the presence of a pseudobranch. But this organ in Bulinus is 

 different from the pseudobranch in Planorbidae, being in the form of folds 

 or ridges while in the Planorbidae it is smooth and leaf-like. There are also 

 differences in the genitalia, principally in the penial complex. These differ- 

 ences suggest that Bulinus, Physopsis, and other related groups should 

 form a separate family Bulinidae. This has been recognized by Germain 

 in his mollusks of France (1931) and by Larambergue in a recent publica- 

 tion (1939). The Indian genus Indoplanorbis has been shown by the latter 

 author to be related to Bulinus and its place appears to be with the 

 Bulinidae. 



Subfamily PLANORBINAE H. A. Pilsbry, 1934 



The subfamily of H. and A. Adams is equivalent to the family Planorbidae 

 as now recognized by systematists. In the Planorbinae the prostate diver- 

 ticula are all simple sacs placed in a single row along the whole length of a 

 long prostate duct which is separated from the sperm duct into which it 

 enters. The ovotestis has the diverticula arranged in a double row. An 

 apparent exception is found in tiie genus Australorbis where the single row 

 of glands is placed directly on the sperm duct and the ends of the prostate 

 diverticula are branched. The kidney is usually rounded and without a 

 superposed ridge. Here again Australorbis is an exception, having a ridged 

 kidney as in Helisoma. 



Tvpe genus Planorbis Geoff roy. 



There is considerable variation among the different genera grouped in 

 Planorbinae, principally in the jaws, the radulae, and the presence of a 

 penial stylet. These differences may be tabulated as follows: 



Radula with serrated marginals placed hijih up on the reflection: Planorbis, 

 Bathyomphahis, Anisms, Gyraulus, Armiger. 



Radula with claw-like marginals on a long reflection: Australorbis, Tropicorbis. 



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