164 DE. J. D. MACDONALD ON THE 



C. Habit. Estuary and marine. 



Analogy of Shell-characters. Illustrative Genera. 



(absent Oncidium. 

 ("internal 



present \ f patelliform Siphonaria. 



[external s • ■■ f inoperculate ... Auricula. 

 ^spira t p ercu i a te Anvphibola. 



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



Suborder 1. Nudibranchiata. 



f Phyllirrhoe. 



(A. Cryptobranchiata -j Limapontia. 



All naked, having no repre- J V ^J^T 



sentative with a shell ... 1 f mtoni(lt 



( B. Phanerobranchia { Doris. 



| Phyllidia. 

 { Diphyllidia. 



Suborder 2. Tectibranchiata. 



qi -,-, f absent Posterobranchcea. 



/-m , i-j \ i , f internal Pleurobranchus. 



(Pleurobranchid*)... \ present { esternal Umbrella. 



on I! [absent Notarchus. 



(W*) {present {?££ Z== j££ 



Q,, Hi ("absent Gasteropteron. 



f internal Philine. 



< Bullld *> [present , 



external 



(Tornatellidse) 



Nucleus in- 1 »». 



volute ] Bulla - 



Nucleus spi- 1 Aplustrum. 



ral f 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. Cyclobranchia. Grill 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 pleuras distinctly differ- 

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

 plates (anaclodontous). 



