42 PYRAMIDULA. 



Genus PYRAMIDULA Fitzinger, 1833. 



Pyramidula FITZ., Systematisches Verzeichniss der im Erzher- 

 zogthume Oesterreich vorkommenden Weichthiere, als Prodrom 

 einer Fauna derselben, p. 95 (for H. rupestris Drap.) 



-f Gonyodisctis and Discus FITZ., 1833; Patula HELD., 18375 

 Delomphalus Ag., 1837; Eyryomphala Beck, 1837 ; etc., etc. 



=Patula of most modern authors. 



Shell openly umbilicated, varying in contour from flattened and 

 disk-like to conoidal. Generally opaque, often rib-striate. Uni- 

 colored, spirally banded or flammulate. Whorls subcylindrical or 

 keeled, the apex generally smooth. Aperture rounded-lunate ; lip 

 simple and thin. Type P. rupestris Drap. 



Animal having the sole undivided; lateral margin of the foot with 

 a distinct border bounded by a groove, the grooves meeting above the 

 tail. No caudal mucous pore. Eye-peduncles long and slender 

 (pi. 14, fig. 40, 46, P. alternata.} 



Genital system lacking all accessory organs; vas deferens and 

 retractor muscle inserted near or at the apex of the penis ; duct of 

 the spermatheca very long; hermaphrodite duct very long, but 

 shortened by its extreme convolution (pi. 11.) 



Jaw arcuate, its component laminae generally compactly soldered, 

 and indicated only by fine striae which diverge slightly from the 

 middle. 



Radula (1) having only the mesocones developed upon central 

 and inner lateral teeth, or (2) having the centrals tricuspid, laterals 

 bicuspid lacking the entocones, marginal teeth similar but with short 

 basal-plates ; this being the usual form. In some species the mar- 

 ginal teeth are multicuspid by the splitting of their ectocones. 



The dentition, as usual, shows considerable variation, even in 

 species otherwise closely related. Asa general rule, the lateral teeth 

 completely lack entocones, differing in this respect from Trachycystis 

 and the Endodonta- Charopa series ; but in the section Helicodiscus, 

 entocones are well developed. The dentition is quite unlike Tra- 

 chycystis in the forms of the marginal teeth. 



The genus Pyramidula consists of dull-colored ground-living snails, 

 species of which occur over the whole northern temperate land area. 

 Its nearest relatives are C/iaropa, Trachycystis and Stephanoda, genera 

 occupying the southern temperate regions of Australasia, Africa and 

 South America respectively. All may be regarded as the remnants 

 of an early fauna, now replaced in the tropics, and to a large extent 



