302 MANUAL OP THE MOLLTJSCA. 



/SAe?/ ovate, sinistrally spiral, thin, polished ; aperture rounded 

 in front. 



Animal with long slender tentacles ; the eyes at their bases ; 

 mantle margin expanded and fringed with long jBlaments. 



P. hypnorum (Aplexa, Fleming) has an elongated spire, and 

 the mantle margin is plain. 



Physopsis^ Krauss, South Africa, has the base of the columella 

 truncated. 



Camptoceras (terebras), Benson, India, has the whorls dis- 

 united, and the peristome continuous. 



Distribution, 20 species. North America, Europe, South 

 Africa, India, Philippines. 



Fossil, 43 species. Wealden — . Britain, France. The largest 

 living species {P. Maugerce, Ecuador ?) is 15 lines in length. A 

 fossil species found at Grignon measures 26 lines, and another 

 equally large occurs in India. 



Ancyltjs, GeofFroy. Eiver-limpet. 



Etymology, Ancylus (agkulos) a small round shield. 



Type, A. fluviatilis, Miiller. PI. XII., Fig. 33 (Patella 

 lacustris, L.). 



Shell conical, limpet-shaped, thin ; apex posterior, sinistral ; 

 interior with a sub-spiral muscular scar. 



Animal like Limnsea ; tentacles triangular, with eyes at their 

 bases ; lingual teeth 37.1.37, in 120 rows, centrals small, laterals 

 with long recurved hooks. 



Distribution, 49 species. North and South America, Europe 

 Madeira. On stones and aquatic plants in running streams. 



Fossil, 8 species. Eocene, Belgium. 



Sub-genera. Velletia (oblonga, Lightfoot), Gray. (Acroloxus, 

 Beck.) 



Shell and Animal dextral ; lingual teeth 40, in 75 rows. 3 

 species. West Indies, Europe. 



Fossil, 2 species. Eocene. Britain, France. 



Latia, neritoides, Gray ; shell limpet-like, interior with a 

 transverse plate, turned u^ and notched on one side. 2 species. 

 New Zealand. 



Planorbis, Miiller. 



Synonym, *' Coret," Adans. 

 Type, P. comeus, PI. XII., Fig. 34. 



Shell discoidal, dextral, many-whorled ; aperture crescentic, 

 peristome thin, incomplete, upper margin projecting. 



Animal with a short, round foot; head short, tentacles 



