364 INVSBTEBRATE MORPHOLOGT. 



1. Order Solenogastres. — Shell represented by scattered calcareous 



spicules. Neomenia, Proneotnenia, Ohatoderma, Dondersia. 



2. Order Polyplacophora. — Shell formed by eight plates on dorsal 



surface of body. Chiton, Trachydermon, Chitondlus. 

 II. Class Gasteropoda. — Visceral hump usually well developed; body 

 asymmetrical; shell univalved and usually spirally coiled, some- 

 times absent; anus not terminal. 



1. Order Prosohranchia. — Ctenidia present, situated in front of the 



heart; auricle in front of ventricle; mantle edge not fused with 

 body. 

 Heart with two auricles; two nephridia {Biotocardiaj. Haliotis, 

 Turbo, Trochus, JYeritina, Pleurotomaria, Fissurella, Patella, 

 Acmcea. 

 Heart with a single auricle and a single nephridium (Monotooar- 

 dia). 

 Dentition taenioglossate. 

 With creeping habit. Cyprma, Paludina, JYatica, Ampul- 



laria, Littorina, Cyclostoma, Calyptrcea, Strombus. 

 With pelagic habit (Heteropoda). Atalanta, Carinai-ia^ 

 Pterotradiea. 

 Dentition ptenoglossate. lantMna, Scalaria, Solarium. 

 Dentition rachiglossate. Fusus, Buccinum, Nassa, Murex, 



Purpura, Oliva, Marginella. 

 Dentition toxiglossate. Terebra, Conus, Pleurotoma. 



2. Order Opisthohrandhia. — Ctenidia frequently absent, when pres- 



ent behind the heart; auricle behind ventricle; mantle when 



present not fused by its edges to body- wall; shell frequently 



absent. 

 Mantle present (Tectibratichia). 



Foot with broad flat sole; with creeping habit. Bulla, Janus, " 

 Aplysia, Pleurobranchus. 



Foot with winglike parapodia, pelagic (Pteropoda). 

 With shell (ThecosoTnata). Limacina, Styliola, Gymbuliopsis, 

 Without shell {Bymnosomata). Pneumoderma, Clione. 

 Mantle not developed {Nudibranchia). Pleurophyllidia, Phyl- 



lirhoe, Limapontia, Doris, JEolis, Facellina. 



3. Order Palmonata. — Ctenidia wanting; mantle fused by its edges 



to body- wall; terrestrial or aquatic. 



Eyes at base of tentacles (Basommatophora). LimncEa Physa 

 Planorbis. 



Eyes at tip of tentacles {Stylominatoplwra). Helix, Li max Arion 

 Vaginula, Baudebardia, Onchidium. 

 III. Class ScAPHOPODA. — Visceral hump developed; bilaterally symmetrical- 

 shell cylindrical, open at both ends. Dentalium, Siphodenta- 

 lium, Cadulus. 



