102 GENERAL HISTORY OF THE INFUSORIA. 



Self-Division ; during which process the cell secretes a more or less sili- 

 cious Connecting Membrane. Eeprobtjction, by Conjugation and the 

 tbrmation of Sporangia. 



Teibe I. Frustules naked ; not imbedded in gelatine nor enclosed in mem- 

 branaceous tubes. 

 SuBTKiBE 1 . Connecting memhrane deciduous ; frustides solitary or du- 

 ring self-division in pairs, rarely in greater numbers, 

 adherent or free, dispersed, or aggregated into a mucous 

 stratum. 

 22 Genera. Epithemia, Eunotia, Cymbella, Amphora, Cocconeis, 

 Coscinodiseus, Eupodiscus, Actinocyclus, Arachnoi- 

 discus, Triceratium, Cyclotella, Campylodiscus, 

 Surirella, Tryblionella, Cymatopleura, Nitzschia, 

 * Amphiprora, Amphiplem^a, Navicnla, Pinnularia, 



Stauroneis, Pleiirosigma. 



SuBTEiBE 2. Connecting membrane subpersistent ; frustules after self- 

 division attached by a gelatinous cushion, or dichoto- 

 mous stipes. 

 7 Genera. Synedi-a, Doryphora, Cocconema, Gomphonema, Po- 

 dosphenia, Ehipidophora, Licmophora. 

 Subtribe 3. Connecting membrane evanescent, or obsolete ; frustides after 

 self -division miited into a compressed filament. 



12 Genera. Meridion, Bacillaria, Himantidiiim, Odontidium, Den- 

 ticnla, Fragilaria, Eiicampia, Achnanthes, Achnan- 

 thidium, Rhabdonema, Striatella, Tetracyclns. 



Subtribe 4. Connecting membrane subpersistent ; frustides after self- 

 division united into a zigzag chain. 



6 Genera. Diatoma, Grammatophora, Tabellaria, Amphitetras, 

 Biddulphia, Isthmia. 



Subteibe 5. Connecting memhrane subpersistent as a silicious annulus ; 

 frustules after self-divisio7i united into a cylindrical 

 filament. 



3 Geneea. Podosira, Melosira, Orthosira. 



Tribe II. Frustules invested with a gelatinous or membranaceous envelope. 

 Subteibe 6. Frond indefinite, mammillate ; frustules scattered. 



1 Genus. Mastogloia. 



Subteibe 7. Frond definite, compressed or globular ; frustules scattered. 



2 Geneea. Dickieia, Berkelejda. 



Subteibe 8. Frond definite, filamentous ; frustules in rows. 



3 Geneea. Encyonema, Colletonema, Schizonema. 

 Subteibe 9. Frond definite, filamentous ; frustules fasciculated. 



1 Genus. Homoeocladia. 



On the Mode of obtaining Diatome^. Peepaeation of Diatomaceous 

 Deposits mixed with Mud oe in the Eossil State. Peeseevation of Spe- 

 cimens. — Many hints on the obtaining of specimens of Diatomea? are scat- 



