CLASSIFICATION. 257 



Mr. Morch believes that mitaralists of the most opposite 

 schools could agree to a scheme of classification which he 

 submits, as follows : 



Sub-Kingdom. 3.— MOLL USCA. 

 Supra-class 1. Phanerogama Latr. (Monotocardia, Morch). 

 Class 1. ANDROGYNA (Hermaphrodita, Latr.\ 



Order I. Geophila, Per (Stylommatophora, A. Schmidt. 



Phyllovora with jaw. Agnatha without jaw. 

 Order 2. Hygrophila ; eyes at the interior base of the tentacles. 



Planorbis, Physa, Limnsea, Siphonaria, Ancylus, Auricula. 

 Order 3. Tectibranchia (Pomatobranchia), Pyramidella 



'connecting with the preceding genus), Obeliscus, Odos- 



tomia, Chemnitzia, Actaeon, Bulla, Aplysia, Notarchus. 



Gasteropteron connecting with the Pteropods. 

 Order 4. Pteropoda. 



1. Gymnosomata. Clione, Pneumodermon. 



2. Thecosomata. Clio, Hyalaea, Limacina, Heterofusus. 

 Order 5. Gymnobranchia. 



1. Pygohranchia. Doris, etc. ; branchiae near the anus. 



2. Pleurognatha.^ Pleurophyllidia, Dendronotus, Tritonia, 



Bornella, ^olis, Glaucus, Phyllirhoe. 

 Order 6. Pellibranchia. Tethys,Chior8ea, Hermaea, Elysia, 



Limapontia, Pelta. 

 All these mollusks are placed at the head of the gastropods 

 by Cuvier. Messrs. Trosehel and Gray arrange them between 

 the Acephala and Patella, considering androgynism as probably 

 a character of absolute inferiority ; but the Acephala have 

 generally separated sexes. 



Class II. DIOICA, Latr. (Exophallia, Morch). 



Order 1. T^nioglossata, Trosehel. 



This is the only division where the family groups and their 

 reciprocal relations do not appear to Morch to be perfectly clear. 

 In any case, it appears incontestable that all mollusks having 

 seven ranges of teeth form a characteristic group. Recently', 

 Trosehel has divided the Taenioglossata into three groups 

 according to the trunk : 



1. Trunk not retractile. 



2. Trunk retractile only by the end. 



3. Trunk retractile from the base. 



These differences appear to oi-iginate solely in the different 

 length of the trunk. The old divisions Holostoraata and Ento- 

 stomata are not very faulty. 



* Dr. Mobius has recently shown that the DoridaB have also lateral 

 j iws, althooigh very little developed. 



17 



