FLEMING. 559 



1. Body with a shell. Cyclobranchia. Patella, 

 Chiton, Chitonellus. 



2. Body naked. Infer obranchia. Phyllidia, Di- 

 phylidia. 



Tribe II. Branchiae simple, and concealed when at 

 rest under a lid. Tectibranchia. 



A. Head furnished with tentacula. 



1. Tentacula four in number, a. Aplysia, No- 

 tarchus. b. Dolabella. 



2. Tentacula, two in number. Pleurobranchus. 



B. Head destitute of tentacula. Bulla, Doridium. 

 Order II. Branchiae internal. 



Subdivision I. Heart entire and detached from the rec- 

 tum. 

 Tribe I. Shell external. 



A. Aperture of the shell entire. 



1. Aperture of the shell closed by a lid. Tur- 

 bonidaa, Neritidse, Trochusidse. 



2. Aperture of the shell exposed. lanthina, 

 Velutina. 



B. Anterior margin of the aperture of the shell 



canaliculated. 



1. Shell convoluted. Cypreadae, Ovuladae, Vo- 

 lutadae. 



2. Shell turreted. Buccinidae, Muricidae, Ceri- 

 thiadae, Strombusidae. 



Tribe II. Shell internal. Sigaretus. 

 Subdivision II. Heart traversed by the rectum. 



Tribe I. Shell ear-shaped. Haliotidae. rHaliotis, 



Padola, Stomatia. 

 Tribe II. Shell conical. Crepiduladae, Capulusidae, 



Fissurelladae. 



DIVISION II. MOLLUSCA ACEPHALA. 



Section I. ACEPHALA CONCHIFERA. 



Order I. Brachiopoda. 



Subdivision I. Shell supported on a fleshy peduncle. 



Lingula, Terebratula. 

 Subdivision II. Shell sessile. Criopus. 

 Order II. Bivalvia. 



Subdivision I. Cloak open. 



Tribe I. Valves closed by one adductor muscle. Pec- 



tenidae, Ostreadae. 



Tribe II. Shell closed by two adductor muscles. 

 Avicularia, Meleagrina, Pinna, Arcadse. 



