SEA-MATS. 430 



The " Sea-mats" are also communities of the Bryozoa. 

 Each side is covered with cells of a somewhat horny na- 

 ture, and each cell marks the place of a bryozoan. 



The Polyzoa comprise two orders : 



PHYLACTOL2EMATA (from the Gr. plmlaktos, guarded, and 

 laimos, throat), or those in which the entrance to the throat 

 is guarded by an epistome, as Pectinella, Cristatella, Pluma- 

 tella, and Pediccllina, etc. 



2. GrYMNOLvEMATA (from the Gr. gumnos, naked, and laimos, 

 throat), or those in which the opening to the gullet is un- 

 covered, as Paludicclld, Escharida, Flustra, etc. 



PRINCIPAL TOPICS CONSIDERED IN CHAPTER IV. 



SECTION I. 



The Mollusca considered as a Branch. Their form, structure, habits, uses, etc. 



Classification. 



SECTION II. 



SUB-SECTION I. 



The Cephalopoda considered as a Class. Their form, structure, size, habits, etc. 



SUB-SECTION II. 

 The Dibranchiata including the Argonaut, Octopus, Cuttle Fishes, etc. defined. 



SUB-SECTION III. 

 The Tetrabranchiata defined. Nautilidae. Ammonitidse. 



SECTION III. 



The Gasteropoda considered as a Class. Shell. Opercnlnm. Teeth. 



Internal Structure. Reproduction. 



1. Prosobranchiata. 2. Pulmonifera. 3. Opisthobranchiata. 4. Hetero- 



poda. 5. Pteropoda. 



SECTION IV. 



The Acephala or Lamellibranchiata or Bivalves considered as a Class. Their 



external form, internal structure, and functions of the various parts. Classifica- 

 tion. 



Sections V., VI., and VII. treat, respectively, of the Tunicata, Brachidpoda, and 

 the Polyzoa or Bryozoa, -their form, structure, etc. 



