NATURAL CLASSIFICATION OF THE GASTEROPODA. 165 



Suborder 4. Cirrobranchia. Gills two, symmetrical, tufted on the back of 

 the neck. 



Ex. Dentalium, Entalis. 



Order II. Eaphidoglossa. Teeth in numerous longitudinal series, the central 

 5.1.5, variable in form ; lateral very numerous, more slender, curved at the tip. 

 — Gray. 



Suborder 5. Dicranobranchia. Gills two, symmetrical on the back of the 

 neck. 



Ex. Deridobranchus (a naked form), Scutus, Emarginula, Puncturella, Fis- 



Suborder 6. Schismatobranchia. Gills in two plumes on the left side of the 

 gill-cavity ; body and shell spiral. 



Ex. Teinotis, Padollus, Haliotus, Scissurella. 



Suborder 7. Scutibranchia. Gills in a spiral line on the left side ; body, 

 shell, and operculum spiral. 



Ex. Stomatella, Trochus, Turbo, Eotella, Nerita, Neritina, and Navicella. 



Suborder 8. Pseudobranchia. Having no distinct gill, being in reality 

 pulmonate. 



Ex. Helicina, Proserpina, Ceres. 



As to the propriety of the application of the term Pulmonata 

 to the terrestrial monoecious Grasteropoda there need be no ques- 

 tion ; but to justify the use of the second subordinal term 

 Pulmobranchiata the following reasons may be adduced. 



1st. Siebold mentions that the raised vascular network of the 

 lining of the pulmonary cavity is coated with cilia in the aquatic 

 species, and he further says that he found ciliated epithelium in 

 the pulmonary cavity of the Limnceidce, though not in that of 

 Limaos or Avion. Ancylus was formerly placed in the Infero- 

 branchia, though really having no alliance with them; and a simple, 

 probably ciliated enlargement on the left side, concealed under 

 a fold of the mantle, has been accepted and figured as a true 

 branchia by both Treviranus and Vogt. S. Clessin thinks that 

 the Limnceidce normally respire water, though it should be re- 

 membered that water only finds access to the lung-chamber when 

 the animals are very young, though the recorder of this fact (A. 

 Pauly) is of opinion that this may be permanently the case with 

 those species which habitually live in deep water. 



2nd. In the amphibious genus Oncidium, Ehrenberg noticed 

 the occurrence of more than twenty small ramified organs at the 

 posterior part of the back, which he regarded as true branchiae ; 



