3802 MANUAL OF THE MOLLUSCA. 
Shell 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 filaments. 
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. Maugere, Ecuador ?) is 15 lines in length. A 
fossil species found at Grignon measures 26 lines, and another 
equally large occurs in India. 
Ancy1us, Geoffroy. Rivyer-lmpet. 
Etymology, Ancylus (agkulos) a small round shield. 
Type, A. fluviatilis, Miller. Pl. XII., Fig. 33 (Patella 
lacustris, L.). 
Shell conical, limpet-shaped, thin; apex posterior, sinistral ; 
interior with a sub-spiral muscular scar. 
Animal like Limneea; 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 
transyerse plate, turned up and notched on one side. 2 species. 
New Zealand. 
PLANORBIS, Miller. 
Synonym, ‘* Coret,” Adans. 
Type, P. corneus, Pl. 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 
