PLEURODISCIDAE. 179 



long, the penial retractor inserted on it. No penial appendix, 

 but the epiphallus has internal complications in the form of 

 spiral ridges. Spermatheeal duct long. Prostate gland about 

 as long as the uterus, composed of many narrow, separate 

 tubules (PI. 29, figs. 3-5, after Watson). 



This very distinct genus comprises a few species distributed 

 around the eastern basin of the Mediterranean. They are 

 closely similar, and possibly not specifically distinct, but only 

 the Sicilian P. halmei has been dissected. Wenz (Fossilium 

 Catalogus part 21, pp. 1069-1071) recognized three or four 

 middle European Tertiary species as follows : 



Pleurodiscus falcifertjs (Bttg.), Helix (Patula) falcifera 

 Boettger, 1870. Upper Miocene, Aquitanian, near Ulm; 

 Burdigalian, Tuchorschitz. Said to be the same as P. 

 orbicularis. 



P. FRici (Klika), Patula (Anguispira) frici Klika, 1891. 

 Upper Oligocene, Warzen, Czechoslovakia. 



P. MAMiLLATUS (Andreac), Pyramidula mamillata Andreae, 

 1904, Upper Miocene, Oppeln. 



P. ORBICULARIS (Klein), Helix orbicularis Klein, 1846. 

 Upper Miocene, near Ulm. 



Pleurodiscus balmei (Pot. & Mich.). Plate 25, fig. 15. 



The shell is depressed with convex spire, umbilicate, the 

 umbilicus contained about 4^ times in the diameter, some- 

 what well-like, contracting but slowly within. Whorls convex, 

 slowly increasing, the last rounded; suture deeply impressed. 

 Buff, the base pale or whitish. The apical 2y^ whorls are 

 nearly smooth and glossy; following whorls dull, rib-striate, 

 the riblets narrow, 3 to 4 in one mm. on the last whorl, a few 

 fine striae in the intervals. Aperture but slightly oblique. 

 Peristome thin, blunt, the basal margin straightened or 

 slightly curving forward, columellar margin dilated. 



Height 5.5 mm., diam. 9.5 mm. ; 5% whorls. 



Height 6.3 mm., diam. 11 mm. ; 6 whorls. 



Sicily: Monte Pellegrino, near Palermo, type loc. ; Malta 

 (Caruana) ; Sardinia near Laconi; Italy at Reggio in 

 Calabria ; Algeria. 



