Subfamilies, Genera, and Subgenera — Recent and Fossil 85 



Some of tlie species of Tropicorbis have been heretofore placed in the 

 genus Planorbula because of the presence of lamellae within the aperture. 

 These lamellae have the same general position in the two groups but the 

 lower palatal lamella in Planorbula points upward while in Tropicorbis it 

 points slightly downward. The basal lamella is also usually more massive 

 in Planorbula than in Tropicorbis (plate 76, figs. 7, 8, 9). Planorbula, how- 

 ever, has a very different form of genitalia which removes it from 

 the Planorbinae and places it, witii Menctus, in a separate subfamily, 

 PIanorl)ulinae. 



The relationshij) between the South American Tropicorbis and certain 

 species in Africa is quite remarkable and has been emphasized by Pilsbry 

 (1934, p. 54). Tw^o African species (adowensis and pfcifferi) have been 

 dissected and the genitalia are very similar to the same organs in Tropi- 

 corbis. The African forms may be placed in Afroplanorbis of Thiele, at 

 least, until more is known about other species of the African fauna. This 

 relationship is discussed at greater length under the description of the 

 genus Afroplanoi'bis. 



\\\u\e the anatomy of the several group forms is similar, there are 

 variations in the shell which seem to warrant a division of the genus into 

 three subgenera or sections. These are indicated below. 



Subgenus TROPICORBIS SS. 



Type Planorbis orbiculus Morelet 



Shell orbicular, the whorls increasing gradually in diameter, the last whorl 

 not notably expanded. Apertural lamellae never present at any stage of 

 growth. 



Subgenus OBSTRUCTIO Haas, 1939 



Type by original designation, Plauorbis jancircnsis Clessin 



Shell orbicular, whorls increasing slowly in diameter. Aperture with 

 lamellae during some stage of the growth of the shell (plate 76, fig. 7) . 



Subgenus LATEORBIS F. C. Baker, New Subgenus 

 Type F^lanorbis pallidas C. B. Adams 



Shell with whorls rapidly increasing in diameter, the body whorl notably 

 enlarged. Aperture never with lamellae. 



Species Considered as Valid. The species and races believed to group 

 under the three subgenera of Tropicorbis are tabulated below. 



TROPICORBIS 



orbiculus (Morelet) 

 may a (Morelet) 

 havaneiisis (Pfeiffer) 

 philipjnanus (Danker) 

 heloicus (Orbigny) 

 tepicensis (Martens) 

 gracilcntus (Gould) 

 peregriniis (Orbigny) 

 chile nsis (Clessin) 

 77}eridaensis (Preston) 

 bourcardianus (Preston) 

 ce7itimetralis (Liitz) 

 fieldi (Tryon) 



OBSTRUCTIO 



jnneiren.sis (Clessin) 

 denticns (Morelet) 

 d('ntie7is ca7i7iarum 



(Morelet) 

 obstructus (Morelet) 

 ob>itructu>< donbilli 



(Tristram) 

 obstruct)is auodontus 



(Pilsbry) 

 dentifcrus (C. B. Adams) 

 deciivis (Tate) 

 paparyensis (F. Baker) 

 nigrilabris (Lutz) 

 albica7is (Pfeiffer) 



LATEORBIS 

 pallidus (C. B. Adams) 

 nisei (Dunker) 

 straniiiieus (Dunker) 

 pete7iensis (Morelet) 

 isthmicus (Pilsbry) 

 decipie7ii< (C. B. Adams) 

 pedri7ius (Miller) 

 cano7iicus (Cousin) 

 irigyrus (Philippi) 



