46 The Molluscan Family Planorbidae 



It has been possible to recognize four subfamilies of the family Planor- 

 bidae based on fundamental anatomical differences, and all of the genera, 

 as far as they have been examined, readily fit into this subfamily classi- 

 fication. A few groups, as Taphius, Biomphalaria, Platytaphius, and Tro- 

 chorbis, are still unknown anatomically, but it is believed that when 

 examined they will be found to fit into this classification. Many species 

 of the family still remain of wliich the animal characteristics are unknown 

 and it is possible that new genera or subgenera will need to be made for 

 their inclusion. It is confidently believed that the classification herein 

 presented will form a reliable foundation on which to build future knowl- 

 edge which may be obtained concerning this interesting family. 



ANATOMICAL KEYS TO GROUPS* 



Key to Subfamilies 



la. Prostate a single row of diverticula usually placed on a separate prostate duct. . .2 



b. Prostate with multiple diverticula usually placed on the sperm duct 3 



2a. Vergic sac with flagella Segmentininae (see p. 47) . 



b. Vergic sac without flagella Planorbinae (see p. 46). 



3a. Prostate forming a fan-shaped pattern in cross section, penial gland duct on 

 outside of preputium, ovotestis consisting of several diverticula arranged 



fanwise Helisomatinae (see p. 47). 



b. Prostate forming a finger-shaped pattern with few diverticula, penial gland duct 



inside preputium, ovotestis with paired diverticula. .. .Planorbulinae (see p. 48). 



Key to Genera of Planorl)inac+ 



la. Prostate diverticula on separate duct, simple, unbranched at end 2 



b. Prostate diverticula not on separate duct, branched at 



end Aiifitralorhift (see i). 90). 



2a. Verge with .stylet, outlet of sperm canal at side 3 



b. Verge without stylet, outlet of sperm canal at end 6 



3a. Shell with many closely coiled whorls not increasing greatly in diameter 4 



b. Shell with few loosely coiled whorls rapidly increasing in diameter 5 



4a. Left side of shell flat without central depression Anisus s.s. (see p. 57). 



b. Left side of shell with deejily excavated 



depression (Subgenus) Bathijomphnlus (see p. 62). 



5a. Left side of shell with rounded whorls on a plane surface. . .Gi/m»/i<.s s.s. (see p. 66). 

 b. Left side of shell with whorls depressed as though reamed 



out (Subgenus) Torquis (see p. 72) . 



6a. Vergic sac le.ss than one-fourth length of preputium Planorhis (see p. 51). 



b. Vergic sac longer than preputium 7 



7a. Vergic sac about as long as preputium, shell 5 mm. or more in diameter, 



not costate 8 



b. "\>rgic sac much longer than preputium. shell 3 mm. or less in diameter, 



usually costate Anniger (see p. 75) . 



8a. Species inhabiting Africa Afroplanorbis (see p. 86) . 



b. Species inhabiting America Tropicorbis s.s. (see p. 85) 9 



*In using this type of alternative key the options are always arranged in couplets, the contrasting 

 conditions being arranged as 'a' and 'b' under the same numeral. The reader always starts with la. 

 If the description under la fits the specimen or concept under consideration, the numeral at the end 

 of that line indicates the next couplet to be tried (except in those instances where la leads directly 

 to an identification). If the .statement under la does not fit, the alternative under lb should, and so 

 on through tile key until a group name is reached at the end of one of the options. This form of 

 continuous and consecutive key is less confusing than the type in which descriptions to be compared 

 are widely separated from each other and does not offer the technical diflScuIties of composition 

 inherent in the indented or step form of key. — H.J.^'-C. 



tSome subgenera which have distinctive morphological characters are included in this key and in all 

 succeeding keys to genera. 



