164 



DE. J. D. MACDONALD ON THE 



Shell .,, 



C. Habit. Estuary and marine. 

 Analogy of Shell-characters. 



Illustrative Genera. 

 Oncidium. 



{ internal 



< f patelliforra Siphonaria. 



I external < • -, f inoperculate ... Auricula. 

 { ^ \ operculate Amphibola. 



Order II. Apneumonophora (having no air-chamber). 



Suborder 1. Nudibranchiata. 



{Phyllirrhoe. 

 Limapontia. 



( Eolis 

 Tritonia. 



( B. Phanerobranchia \ Boris. 



Phyllidia. 

 \ Diphyllidia. 



sentative with a shell 



Shell 



Suborder 2. Tectibranchiata. 



{absent Posterobranchcea. 



f internal Pleurobranchus. 



present < , , TT , 77 



r [external Umbrella. 



^i 11 [ absent Notarchus. 



, A , • -i v \ finternal Aplysia. 



(Aplysiadae) j present ( external jfj^ 



{ni 11 f absent Gasteropteron. 



,-p iivq \ \ finternal Philine. 



( } Ip"»«* . , ( Nucl ?" s in - ) Bulla. 



[ external J volute J 



Nucleus spi- \ Aplustrum. 



(Tornatellidae) L ral J Tornatella. 



Subdivision II. Lingual membrane strap- or ribbon-like *. 

 Order I. Heteroglossa. Teeth in five to eight longitudinal series, variable 

 in form, the larger ones with opaque tips. Foot without any lateral fringe. 

 Shell symmetrical. — Gray. 



Suborder 1. Polyplacophora. Shells forming a linear imbricate series on 

 the middle of the back. 



Ex. Chiton, Chitonellus, &c. 



Suborder 2. Oyclobranchia. Gill lamellar, forming a more or less complete 

 ring beneath the mantle. 

 Ex. Patella, Patina. 



Suborder 3. Cervicobranchia. Gill single, to the left on the back of the 

 neck. 



Ex. Tectura, Gadina, Lepita. 



* Dentition typically multiserial, with rhachis and pleurae distinctly differ- 

 entiated, the dental processes being recurved from the fore part of the basal 

 plates (anaclodontous). 



