VALVATA. 31 



The respiratory organs of the Valvatidae are very 

 singular. When the animal whilst crawling is ex- 

 tended, the gill is protruded beyond the edge of the 

 mantle in the form of an elongated, conical process 

 called the branchial plume, which is provided on each 

 side with a number of slender, spirally-twisted fila- 

 ments, causing the organ to appear like a feather ; the 

 mantle itself, also, is furnished on the right side with 

 a filament which somewhat resembles a tentacle and 

 is, as well as the other organ, used for respiration. 

 This is the branchial appendage. 



The animals belonging to this family are grega- 

 rious. They frequent sluggish waters, and feed upon 

 aquatic plants. Both sexes are united in the same 

 individual when it has arrived at maturity, but in 

 the early stages of its growth it is male or female 

 only. The Valvatidce very frequently attach their 

 shells to the cases of the larvae of Phrygania, popu- 

 larly known as Caddice-worms. One genus only be- 

 longs to this family, viz : 



VALVA'TA* MULLER. 



Body spiral, capable of being entirely contained within the 

 shell ; eyes almost sessile, placed on the inner side of the ten- 

 tacles at their base. 



Shell dextral ; umbilicus deep ; operculum horny. 



i. VALVATA PISCINA'LIS,! MULLER. PL. IV. 



Body transparent, of a light yellowish-grey; tentacles thickish, 

 placed rather near to each other ; eyes large, round, black ; snout 

 narrow, yellowish-grey, with a tinge of brown underneath, finely 

 wrinkled ; branchial plume with 14 filaments on each side 



* Valved (i. e. having an operculum). 

 t Living in fish-ponds. 



