GASTEEOrODA. 257 



She m'ntito, cylindrical, truncatGd ; wliorls striated trans- 

 versely; aperture oval, entire; peristome continuous; operculum 

 sub -spiral! 



Animal with short, diverging triangular tentacles; eyes: 

 centrally behind ; head bi-lobed ; foot short, rounded at each 

 end. (Forbes.) 



The triincatellce are found on stones and sea-weeds between 

 tide-marks, and survive many weeks out of the water. (Lowe.) 

 They walk by contracting the space between their lips and foot, 

 like the geometric caterpillars. (Gray.) They are found semi- 

 fossil along with the human skeletons in the modern limestone 

 of Guadaloupe. 



Distrihution, 15 species. West Indies, Britain, Mediterranean, 

 Eio, Cape, Mauritius, Philippines, Australia, Pacific. (Cuming.) 



? LiTHOGLYPHUS, Megcrle. 



Tijpe, L. fuscus (PI. IX., Pig. 22). 



Shell naticoid, often eroded; whorls few, smooth; aperture 

 large, entire ; peristome continuous, outer line sharp, inner lip 

 callous; umbilicus rimate; epidermis olivaceous; operculum 

 pauci-spiral. 



Distribution, 5 species. Europe and Oregon. 



Family VII. — Paltjdinid^. 



Shell conical or globular, with a thick, olive-green epidermis ; 

 aportiu-e rounded ; peristome continuous, entire ; operculum 

 horny or shelly, normally concentric. 



Animal with a broad muzzle ; tentacles long and slender ; 

 eyes on short pedicels, outside the tentacles. Inhabiting fresh 

 waters in all parts of the world. 



Palttdina, Lam. Eiver-snail. 



Etymology, palus {paludis), a marsh. 



Synonym, Yiviparus, Gray. 



Type, P. Listeri (PI. IX., Fig. 26). (P. vivipara. Fig. 68.) 



Shell turbinated, with round whorls ; aperture slightly angular 

 behind ; peristome continuous, entire ; operculum horny, con- 

 centric. Animal with a long muzzle, and very short eye- 

 pedicels ; neck with a small lappet on the left side, and a larger 

 on the right, folded to form a respiratory siphon ; gill comb -like, 

 single; tongue short; teeth single, oval, slightly hooked and 

 denticulated ; uncini 3, oblong, denticulated. The paludinro are 



