PECTINIBRANCHIATA. 395 



Scutum (Scutus) Montfort (Parmophorus~B\a,inv.), Australia, shell partly covered 

 by mantle ; Cemoria Leech, Rimula Defrance. Propilidium.Forbes and H., and 

 Gocculina Ball, allied here. 



Section B. With one (left) ctenidium (Azyg abranchiate}. 



Fain. 4. Trochidae. Visceral sac and shell coiled in a spiral j eyes open ; 

 operculum horny ; with head-lobes between the tentacles. Trochus L. ; Marga- 

 rita Leach (Fig. 312) ; .Monodonta Lam. 



Fam. 5. Stomatiidae. Spire of visceral sac and shell reduced. Stomatella 

 Lam. ; Gfena Gray ; Broderipia Gray ; Stomatia Lam. , without operculum ; 

 Phaneta Ad., fluviatile. 



Fam. 6. Delphiuulidae. Visceral mass and shell spiral ; no cephalic lobes. 

 Delphinula Lam. ; Cyclostrema 

 Marryat. 



Fam. 7. Liotiidae. Liotia 

 Gray. 



Fam. 8. Turbinidae. Visceral 

 sac and shell spirally coiled ; 

 epipodial tentacles ; calcareous 

 operculum. Turbo L., top-shell. 

 Phasianella Lam., pheasant-shell ; 

 Mdlleria Jeffreys. 



Fam. 9. Neritopsidae. Neri- 

 topsis Grateloup. 



Fam. 10. Macluritidae. Ma- 

 clurea Lesueur. 



Fam 11 Neritidae. Epipo- FlG - *& Margarita greenlandica (after Pelseneer, 

 dium little developed, without JT,^ ^;eacl ; ^ anterior epipoclal lobes ; 



3 foot ; k pigmented eminences at the base of the 



tentacles ; a cephalic penis ; cal- epipodial tentacles 5; 6 visceral sac. 



careous operculum ; eyes stalked. 



Nerita L. ; Neritina Lam. , chiefly brackish water and fluviatile ; land species 

 are known ; N. fluviatilis Miiller, British rivers. Theodoxia Mont. ; Sinaragdia 

 Issel ; Septaria Fer. 



Fam. 12. Titiscanidae. Shell and operculum absent. Titiscania Bergh ; 

 T. limacina Bergh., Pacific Ocean. 



Fam. 13. Helicinidae. Epipodium without tentacles ; branchia absent, 

 mantle cavity transformed into a pulmonary chamber ; heart with a single 

 auricle, not traversed by the rectum. Operculum without apophysis. Terrestrial. 

 Helicina Lam. , Central America and Bahamas ; Hydrocena Parreys ; Georissa 

 Blanford. 



Fam. 14. Proserpinidae. Branchia replaced by pulmonary cavity; mantle 

 partly reflected over shell; operculum absent. Terrestrial. Proserpina Gray, 

 Cuba, Jamaica, Venezuela ; Ceres Gray, Mexico. 



Sub-order 2. Pectinibranchiata (Ctenobranchia, Monotocardia). 



Ctenidium monopectinate, generally without labial commissure. 



The nerve-collar is behind the buccal mass, and there is no labial 

 commissure (except in Paludina and Ampullaria). The single 

 osphradium is often pectinate, and well differentiated. The eye is 

 always closed. Otocysts with otolith (except Paludina, Valvata, 



