MALACOZOA. GASTEROPODA. PECTINIBRANCHIATA. 51 



Asiphonata. Without a Branchial Tube. 



Family I. — Paludixina. 



Body elongated, spiral, with a spiral shell ; two coni- 

 cal, elongated tentacula, having the eyes situated at then- 

 base externally ; the aperture of the shell oval, with the 

 peristome complete ; a corresponding operculum. The 

 name from the Genus Pallidum. 



Genus 1 . Paludina. — Animal with the tentacula taper- 

 ing, of moderate length. Shell oval, with the peristome 

 thin ; operculum horny, Pdlus, a marsh. 



1. Paludina vivipara. — Shell oval, rather thin, with 

 the turns very convex, horn-coloured, with three spiral 

 brown bands. Vivqwrus, producing live young. 



Genus 2. Bythinia. — Animal with the tentacula slender 

 and elongated. Shell oval, with the peristome thickened 

 internally ; operculum calcareous. Name, I suppose, 

 from (3v6los, dwelling in the deep. 



1. Bythinia tentaculdta. — Shell ovato-conical, of five 

 convex turns ; the mouth nearly half the entire length. 

 Tentaculdtus, having remarkable tentacula. 



Family II. — Naticina. 



Body elongated, spiral, with a spiral shell ; two conical 



tentacula; eyes on short pedicels at the outer side of 



their base ; the aperture of the shell roundish ; a horny 



or calcareous operculum. Name from the Genus Ndtica. 



<jenus 1. Natica.-— Shell globose or oval, spiral, urn- 

 bilicate ; the aperture roundish or semicircular, with the 

 outer Up thin, the inner partly covering the umbilicus. 

 Nates, a buttock or prominence. Lamarck. 



1. Ndtica monilifera. — Shell globose, of five very con- 

 vex turns, having a series of purple spots near their 

 upper margin ; spire very short and convex. Monilis, a 

 necklace or string of beads ; fero, to bear. 



2. Ndtica rutila. — Shell subglobose, rather broader 

 than high, of four very convex turns, dull-red, with a 

 white band margining the narrow canaliculate suture ; 



