100 TRACHELIPODA. 



convex, modifying the spiral cavity; aperture subrotund, 

 ovate, or oblong, angulated above ; margins of outer and 

 inner lips united, acute, but not reflected; an orbicular 

 horny operculum. 



Paludina vivipara. — The Viviparous Paludina. Plate 

 XIII. fig. 3. Thin, ovate, ventricose, wrinkled longitudi- 

 nally ; body with three or four brown bands ; covered with 

 an olivaceous epidermis. One inch and a half long. Inhabits 

 the rivers of Europe. 



Genus Q2.^\ khY kH k.—Muller . 



Generic Character. — Shell discoid or conoid, umbilicated ; 

 volutions cylindrical, not modifying the spiral cavity ; mar- 

 gins united and acute ; operculum orbicular. 



Valvata piscinalis The Pond Valvata. Plate XIII. 



fig. 4. Globular, conoid, somewhat trochus-shaped, deeply 

 umbilicated; apex obtuse; longitudinally wrinkled; covered 

 with a greenish-yellow epidermis. One-fourth of an inch 

 long. Inhabits the rivers and lakes of Europe. 



FAMILY VIII. MELANIACEA. 



Fluviatile, operculated shells ; with the margins of the 

 aperture disunited ; the outer lip always thin-edged ; the 

 animals respire water only, and are provided with two 

 tentacula. 



Genus 63 'PIRE'N A.— Lamarck. 



Generic Character. — Shell turreted; aperture longitudi- 

 nal ; outer lip acute, with a distinct siims at the base, and 

 another at its junction with the body; base of the columella 

 turned towards the right ; a horny operculum. 



Pirena terehralis. — The Wimble Pirena. Plate XIII. 

 tig. 7. Subulate, longitudinally striated ; outer lip expanded ; 

 covered with a deep blackish-brown epidermis ; aperture 

 white. Three inches long. Inhabits the rivers of India. 



