540 



MOLLUSCA 



PHYLUM VI 



Lacuna Turton (Fig. 927). Like the last, but thin, small, with an excavated pillar. 

 Tertiary and Recent. 



Fic. y2G. 



Littorina Utorea (Linn.). 

 Post-Pleistocene ; Lsle of 

 Skaijto. 



Fig. 927. 



Lacuna (?) basterotina 

 Bronn. Miocene ; Stein- 

 abrunn, near Vienna. 



Fig. 92S. 



Fossarus costatus Brocchi. Pliocene ; 

 Liraite, Tuscany. 



Lacunella Deah. Eocene. Litiopa'Rang; PlanaxisLnm.; QnoyiaBesh. Tertiary 

 and Recent. The families Litioindae and Planaxidae are usually recognised. 



The genus Fossarus Phil. (Fig. 928) forms, according to Fischer, a separate family, 

 Fossaridae. It occurs in the late Tertiary and Recent. 



Family 3. Cyclostomatidae Menke. 



Shell extremely variable in form, turbinate to discoidal, sometimes turrcted, covered 

 with epidermis. Aperture circular, with usually entire peristome. Operculum horny or 

 calcareous, spiral. Terrestrial. Cretaceous to Recent. 



Like the pulmonate snails, the animal possesses a respiratory cavity. But in 

 other respects they approach the Littorinidae very closely, which latter . forms also 

 have the gill mucli reduced. The shell haljit is excessively variable. There are more 

 than 600 Recent species distributed thi'oughout all parts of the globe, but the majority 



Fl(i. 929. 



Cydostoma hi- 

 sidcatum Zicten. 

 Miocene; Brmin- 

 gen, near Ulin, 

 Wurtemberg-. 



Fig. 930. 



Pomatvis la}ieUiirti 

 (Thomas). Helix 

 Beds (U])per Oligo- 

 eene); Hochheim, 

 near Wiesbaden. 



Fic. 931. 



Cyclotus exaratus Sandb. 

 Upper Eocene ; Pngnello, 

 Italy. Shell and operculum 

 (after Sandberger). 



Fig. 932. 



Strojihostoma nnom- 

 phala Capellini. Oligo- 

 cene ; Arnegg, near 

 Ulm, Wiirtembeig. 



of these are tropical. Fossil forms are found in fresh-water deposits as old as the 

 Middle Cretaceous. 



Gyclostomus Montf. (Fig. 929). Turbinate, with calcareous spiral operculum. 

 Tertiary and Recent. 



Otopoma, Tudora Gray. Tertiary and Recent. 



Megalomastoma Guild. Turbinate to chrysalis-shaped, usually smooth. Peristome 

 with thick margins ; outer lip reilected. Operculum horny. Cretaceous to Recent. 

 M. mumia (Lamarck). 



Pomatias Studer (Fig. 930). Turreted, transversely striated, with reflected 

 margins and calcareous operculum. . Tertiary to Recent ; palearctic 



Leptopoma Pfeiff.; Gyclophorus Montf; Graspedopoma Pfeiff ; Gyclotus Guilding 

 (Fig. 931), etc. Upper Cretaceous. These genera are considered to form a distinct 

 family, Gyclophoridae. Strophostoma Desh. (Fig. 932). Upper Cretaceous to Miocene. 



