A Xew Classification of the Family Planorbidae 47 



Oil. Shell with closely coiled whorls slowly increasing in diameter, orbicular 10 



b. Shell with loosely coiled whorls rapidly increasing in 



diameter (Subgenus) Latcorhis (see p. 85). 



10a. Ajierture without internal lamellae at any stage of 



growth Tropicurhi.s s.s. (see p. 85) . 



b. Aperture with internal lamellae during a i)art of the shells 



growth (Subgenus) Ohstrurtio (see p. 85). 



Key to Genera of Segnientininae* 



la. Genitalia with penial gland in preputium 2 



b. Genitalia without penial gland in preputium 5 



2a. An external penial gland duct on preputitmi 3 



b. Without penial gland duct on preputium 4 



3a. External duct very short, half as long as preputium; penial gland a simple 

 cup attached 'to wall of preputium; flagella more than twice as long as 



vergic .sic, sausage-shaped, attached to short ducts Intha (see p. 112). 



b. External duct about four times as long as preinitium; penial gland sac-like, 

 bifurcated; flagella consisting of small cylindrical sacs attached to very 



long ducts Pingiella (see p. 109). 



4a. PreiHitiinn narrow, club-shaped; vergic sac longer than preputium; verge 



slender with vergic appendage at end Segmentina (see p. 96). 



b. Preputium wide, pear-shaped; vergic sac shorter than preputium; verge wide 



at upper part, without penial appendage Hippeutis (see p. 100). 



5a. Flagellum long and narrow; vergic sac and preputium of about the same 



length ; shell more than 5 mm. in diameter 6 



b. Flagellum wide and short; vergic sac about twice as long as preputium; shell 



very small, 1.5 mm. in diameter Acrorbis (see p. 121). 



6a. Flagellum as long as penial complex, swollen or club-.?haped at 



sununit Polypylis (see p. 104) . 



b. Flagellum shorter than penial complex, not swollen at summit, often bifid 



at the end Drepanotrema (see p. 114) 7 



7a. Shell with rounded pcrijihery Drepanotrema s.s. (see p. 118). 



b. Shell with angulated or carinated i>erii)hery. . (Subgenus) Fo.<>!^ulorbis (see !>. 118). 



Key to Genera of Helisomatinae+ 



la. Prejiutium with i)enial gland but without penial duct ... .PlnnorbariJi^ (.see p. 166). 



b. Preputium with external penial gland duct 2 



2a. Penial complex with one retractor muscle 3 



b. Penial complex with two retractor muscles 6 



3a. Penial complex with but little constriction between vergic sac and preputium; 



Ijenial gland duct about half as long as preinitium. . .Hclisoma s.s. (see p. 124) . . .4 

 b. Penial complex with notable constriction between vergic sac and preputium; 



penial gland duct as long as the jn-eputium. .. (Subgenus) Scminolina (seep. 129). 

 4a. Penial complex with vergic sac and preputium equal in length, the preputium 

 much wider than the vergic sac; jjenial gland duct several times as long as 



preputium, in a coil between vergic sac and preputium 5 



b. Penial complex with vergic sac shorter than the preputium. which is elongate; 



penial gland short and thick, not longer than preputiimi 6 



5a. Shell with simple aperture, not campanulate. .. (Subgenus) Picrostnna (see p. 134). 

 b. Shell with campanulate or bell-shaped aperture (Subgenus) Planorbella (seep. 150). 

 6a. Penial duct on outside of preputium very short, slender, placed between 

 vergic sac and preputium; penial gland an elongated cup with wide 



a]ierture Carinifex (see p. 154). 



b. Penial duct twice as long as in 6a, thick, wide, extending from upper part of 

 ju'eputium to vergic sac; penial gland pijie-shaped, with a long "stem" at- 

 tached to a short "bowl" Parapholijx (see p. 161). 



*One subgenus is included among the groups differentiated in tliis key. 

 tSeveral subgenera are also differentiated in this key. 



