892 



THE ANIMAL CARRIERS OF DISEASES 



Subclass II.: Euthyneura Spengel. 

 Synonym. — Platymalakia von Jhering. 



Definition. — ^Gastropoda monoecius with radula possessing uniform teeth 

 on each side of the median tooth. Head usually with two pairs of tentacles. 

 Detorsion of organization when adult. 



Classification. — 



A. Marine forms with aquatic respiration — Opisthobranchiata. 



B. Aerial or fresh-water (exceptionally marine) forms, with pallial cavity, 



but no ctenidium. No free larval form — Pulmonata. 



Order Pulmonata Cuvier. 

 This order is divided into two suborders : — 



A. Aquatic forms, with a single pair of tentacles — Basommatophora. 



B. Terrestrial forms, with two pairs of tentacles — Stylommatophora. 



Suborder Basommatopliora. 

 Definition. — Pulmonata with an external shell and a single pair of well- 

 developed contractile but not invaginable tentacles, at the bases of which lie 

 the eyes. 



Classification. — There are some eleven families, but only the following 

 concern us: — 



A. Shell thin, dextral; no inferior pallial lobe — LimnceidcB . 



B. Shell sinistral; inferior pallial lobe prominent — Planorbidcs. 



Family Limnseidae Broderip. 



Definition.— Basommatophora with shell thin, horn coloured, and capable 

 of retaining the whole animal when retracted. Aperture single; lip sharp, 

 No inferior pallial lobes. Tentacles angular and fiat. 



Remarlis. —These molluscs are found in fresh water all over the world. 



Type Genus — LimncBa Lamarck. 



Genus Limnsea Lamarck. 

 Definition. — Limnaeidae with spiral shell, m.ore or less elongated, thin pointed 

 spire translucent; body whorl large; aperture rounded; columella obliquely 

 twisted . 



Type Species. — LimncBa stagnalis Linnaeus. 



Other Species. — The hosts of Fasciola hepatica are : — L. truncatula Miiller, 

 Europe, Asia, Africa; L. ouhonensis, Eyd, Sandwich Isles; L. viator, 

 D'Orbigny, South America; L. humilis, Say, North America. 



Family Planorbidae Adams. 



Definition. — Basommatophora with sinistrally coiled shell. In- 

 ferior pallial lobe very prominent, transformed into a branchia; 

 tentacles tapering. 



Classification. — 



A. Shell discoid, branchia not folded — Planorbis. 



B. Shell ovoid, with prominent spire. Branchia not folded — 



Bulinus. 



