122 MALACOZOA. GASTEROPODA. PECTINIBRANCHIATA. 



and communicating externally by a large aperture between 

 the body and the edge of the mantle. 



Some species have a respiratory tube, formed by a 

 prolongation of the margin of the branchial cavity on 

 the left side, and passing along a channel or notch in 

 the shell; but others are destitute of this branchial 

 siphon, and cannot respire without partially emerging 

 from the shell. 



SECTION I.— AS I PH ON AT A. 



Branchial aperture plain; shell with the month eyitire. 



Family I . — Paludinina. 



Animal with the body elongated, spiral, and covered 

 with a shell ; head proboscidiform ; mouth with a small 

 serrulate lingual mass ; two long slender, conical or seta- 

 ceous contractile tentacula ; eyes at the outer side of 

 their base ; orifice of the branchial cavity without tube or 

 canal ; branchiae pectinated or reticulated ; oiifice of the 

 intestine on the floor of the branchial cavity ; sexes 

 separated ; the foot large and depressed. A horny 

 operculum. 



Shell spirally bent, globose, ovate, conical, or discoid, 

 thin, generally covered with an epidermis. 



The species inhabit fresh-water, and occur chiefly in 

 the warmer parts of the globe. 



There is little distinction between this family, and 

 the operculated branchiferous pulmonated Cyclostomina 

 of the first order, of which there are no representatives 

 in our district, and the next family of the Tiu-binina. 



Genus 1. Paludinina. Marsh-Shell. 



Animal elongated, spiral, with the head proboscidi- 

 form ; two contractile, tapering tentacula, bearing the 

 eyes on prominences at the base externally ; the mouth 

 with a small hispid hngual mass ; the foot oval. 



