jio Introduction to Animal Morphology* 



Scries II. Tacnioglossata (3. 1.3), including, 19. Ceri- 

 thiidae foot small, round ; eye near the base of the tentacle ; 

 shell multispiral, slender, without or with periostracum, with 

 small mouth, canalated fore and aft; operculum horny, spiral. 



20. Melaniadce freshwater; shell often corroded, slender, 

 with a thick, dark periostracum ; outer lip of peritreme 

 sharp ; tentacles arch-shaped ; proboscis not retractile. 



21. Pyramidellidse shell oval, or tapering, nucleus clexio- 

 trope ; tentacles broad, ear-shaped ; proboscis retractile ; 

 operculum horny (Stylifcr, Chemnitzia, &c.) 22. Turritel- 

 lidce shell slender, tapering, multispiral ; apex often broken ; 

 peritreme round, simple ; gill single ; foot short ; opercu- 

 lum horny ; Caecum has a tubular, non-spiral shell, with a 

 multispiral operculum. 23. Vermetidse sessile; shell irre- 

 gularly spiral, tubular, frequently fissured (Siliquaria), one, 

 left, pectinate gill. 24. Xenophorida shell lamellose, trochi- 

 form, with many agglutinated foreign bodies in it ; proboscis 

 long ; eyes at the base of the long thin tentacles (Phorus). 

 25. Naticidce shell globular, paucispiral, smooth, short- 

 spireil ; mouth semilunar ; columella swollen ; proboscis, 

 long; eyes may be absent. 26. Kntoconchidae, including 

 a curious parasite existing as a shell-less pouch attached to 

 the calcareous ring of Synapta, only containing sexual organs ; 

 from these develop a naticoid shell, whose further history is 

 unknown. 27. Marsenidaj shell thin, ear-shaped, horny, 

 inoperculatc ; hidden in the foot ; the larval shell is com- 

 pletely shed. 28. Acmaeadae shell and animal limpet-like ; 

 radula long; operculum none; foot large. 29. Capulidse 

 foot as last ; shell patelliform with a trace of a spire, and an 

 internal, lamellar, horseshoe-shaped (Capulus, Calyptraea), or 

 funnel-shaped (Crucibulum), or horizontal, muscular lamella 

 (Crepidula) ; Hipponyx forms a shelly lamina under the foot. 

 30. Littorinidrc foot thick ; eyes at base of tentacles ; oper- 

 culum paucispiral, horny ; mouth entire round ; shell oval ; 

 siphon rudimental. 31. Paludinidae freshwater ; shell 

 oval, with olive-green periostracum, and entire mouth ; oper- 

 culum eccentric, lamellose. 32. Valvatidas freshwater; glo- 

 bular or discoidal, with a tentacle from the mantle; gills 

 projecting out of the mantle cavity ; foot small. 33. Ampul- 



