FAMILY TURBINID^ PALUDINA. 83 



SECTION 5. PECTINIBRANCHIA. 



Animal with gills arranged in parallel rows like the teeth of a comb, within the pulmonary 

 cavity, which has a large opening infr-ont and above, between the edge of the mantle and 

 the body. Two eyes, variously placed, sometimes on pedicles. Sexes separate : the orifice 

 of the female on the right side, at the entrance of, or within the branchial cavity ; the 

 male organ on the right side of the neck, usually very robust and reflected into the bran- 

 chial cavity : vent anterior and on the same side. Tongue often armed with small hooks. 

 Aquatic; usually marine ; a few genera fluviatile. Sn^hi. complete and spiral, variously 

 shaped, almost ahoays external, rarely internal. Opercle complete, rudimentary or none. 



Obs. This section, or order, as it stands in various works, comprises all the spiral uni- 

 valves, and many that are simply conical ; it is consequently the most numerous in species. 

 It corresponds with the Trachelipodes of Lamarck, and the Chismobranches of Blainville. 

 It has been subdivided into three groups, according as the water is introduced to the gills, 

 1, by a membranous appendage ; 2, by a siphon ; and 3, without either. 



FAMILY TURBINID^. 



Animal with two subulate contractile tentacles ; eyes at their base. Fluviatile or marine. 

 Shell variable in form. Aperture rounded or oval ; the edges not disunited, or slightly 

 so : without canal or emargination. Opercle horny or calcareous. 



GENUS PALUDINA. Lainarck. 



Animal : Mouth without teeth, but having in its stead a small prickly lingual mass. Tenta- 

 cles contractile. Foot oval, with a marginal furrow in front. Male organ very large, and 

 retracted through an orifice in the right tentacle near its base. Vent at the extremity of a 

 small tube near the branchial cavity. Shell conoidal, with an epidermis. Whorls rounded 

 or convex : aperture rounded or oval, angulated above : margins of outer and inner lip 

 united, with acute but not reflected edges. Opercle orbicular, horny. 



Obs. The shells of the animals of this genus are distinguished from those of Melania by 

 the simple curvature of the lip at the base, from Cyclostoma by its simple lip, and from 

 Valvata by the form of its aperture. There are numerous species in the Western and 

 Southern States, but very few as far north as this State. 



11* 



