3o8 hitrodudion to Animal Morphology. 



Clithon is spiny ; Navicella is patelloid, with a rudimental 

 operculum. 



§ IV. Ctenobranchiata — gills two, pectinate, in the mantle 

 cavity ; penis present ; never rhipidoglossal. It is divided 

 into two sub-sections, according as the peritreme is entire 

 (Holostomata), or elongated into a canal corresponding to 

 the siphon of the mantle (Siphonostomata). 



Sub-section i. Siphonostomata consists of three series : — 

 I — Taenioglossata, including thefollowingfamilies : — i . Strom- 

 bidae — head with an annulated rostrum ; eye-stalks thick, 

 giving rise to the tentacles when they exist ; outer lip of 

 the shell wing-like ; foot narrow, divided ; outer edge of 

 mantle entire (Strombus), or cleft (Pteroceras) ; spire long 

 in Rostellaria. Terebellum has no tentacles, and unequal 

 eye-stalks. 2. Aporrhaidoe — foot trigonal ; eye-stalks small 

 at the base of the long tentacles ; outer lip of canal expanded; 

 spire long (Aporrhais), or short (Struthiolaria). 3. Pedicula- 

 riadae — irregular shells, parasitic on Mediterranean corals ; eyes 

 sessile atoutersideofthebaseoftentacles. 4. Doliidae — siphons 

 recurved ; foot small, with lateral lobes ; shell ventricose ; eyes 

 on short stalks ; operculum none (Cassidaria, Dolium), or small 

 (Cassis) ; shell usually thick or thin, spirally ribbed (Dolium), 

 in Ficula pear-shaped, with a long canal. 5. Tritoniidae — 

 spiral elongated, with continuous (Ranella), or discontinuous 

 (Tritonium), varices, and long siphonal canal ; foot small : 

 shell sometimes distorted (Persona). 6. Cypraeidae — shells 

 porcellanous, smooth-ribbed (Trivia), or tubercled (Pustula- 

 ria), involute ; tentacles long, subulate ; foot broad ; opercu- 

 lum none ; inner lip of shell corrugated, rarely smooth 

 (Ovulum, Volva). 



Series II. Toxiglossa — radula i . o . i ; siphon with a poi- 

 son gland opening through the hollow teeth. Families 7 : — 

 Conidse — foot with one conspicuous pore ; shell inversely 

 conical, with a long narrow aperture, with simple lips, and 

 nearly flat (Conus), rarely produced spire (Dibaphus) ; pro- 

 boscis and siphon short ; operculum small, unguiculate. 8. Te- 

 rebridae — shell long, multispiral, acute ; mouth and canal 

 small ; siphon long ; operculum ovate, pointed, with apical 

 nucleus. 9. Pleurotomidae — shell fusiform or conical, its 



