British Marine Testaceous Mollusca. 



473 



Diagram of the Synopsis, being a strict one of its genera, in natural position, 

 in respect to the main lines and branches, agreeably to our method. 



Hypothyris. 



Terebratula. 



Megathyris. 



Crania. 



Anomia. 



Pecten. 



Lima. 



Ostrea. 



Mytilus. 



Modiola. 



Crenella. 



Pinna. 



Avicula. 



Area. 



Pectunculus. 



Nucula. 



Leda. 



Galeomma. 



Unio. 



Anodon. 



Cyprina. 



Circe. 



Astarte. 



Isocardia. 



Lucina. 



Turtonia. 

 Kellia. 

 Lepton. 

 Montacuta. 



Cyclas. 



Pisidium. 



Cardium. 



Venus. 



Artemis. 



PuUastra. 



Lucinopsis. 



Mactra. 



Donax. 



Ervilia. 



Tellina. 



Psammobia. 



Syndosmya. 



Scrobicularia. 



Diodonta. 



Anatina, 



Corbula. 



Spliaenia. 



Pandora. 



Nesera. 



Poromya. 



Solen. 



Solenicurtus. 



Gastrochaena. 



Saxicava. 



Venerirupis. 



Petricola. 



Mya. 



Pholas. 



Teredo. 



Xylophaga. 



Dentalium. 



Chiton. 



Patella. 



Acmsea. 



Pileopsis. 



Calyptra2a. 



Fissurella. 



Emarginula. 



Puncturella. 



Haliotis. 



Pleurobranchus. 



Hyalea. 



Spirialis. 



Aplysia. 



Bulla. 



BuUaea. 



Tornatella. 



Limax* 

 Helix 

 Limnea. 

 Cyclostoma. 

 Paludina. 

 Neritina. 

 Littorina. 



Rissoa. 

 Assiminia. 

 Skenea. 

 Trochus. 

 Phasianella. 

 Adeorbis. 

 Turritella 

 Cerithium 

 Aporrhais 

 Csecum. 



Conovulus. 

 Pedipes. 

 Otina. 



Carychium. 



Acme. 



Truncatella. 



Chemnitzia. 



Eulima. 



Aclis. 



Scalaria. 



lantliina. 



Natica. 



Lamellaria. 



Velutina. 



Murex. 



Cypraea. 



Ovula. 



Marginalia. 



Octopus. 



Eledona. 



Loligo. 



Sepia. 



Sepiola. 



Spirula. 



We have made Tornatella tlie point of departure of the branch 

 lines ; because, though it has an operculum, it is from its structure 

 and hermaphroditism much more closely allied to Bulla than 

 either to Cyclostoma on one side, or to Truncatella and the Pyra- 

 midelhdse on the other. The intervention of Limax, Helix, and 



