DIATOMACE^E. 



[ 204 ] 



DIATOMACE^E. 



entangled in the meshes of Confervae and 

 other Algae, or on the submersed stems of 

 the higher plants; these, if fixed to the stems, 

 can only be removed with them; if, however, 

 the masses of Diatomaceae are merely en- 

 tangled in the meshes of their stems, they 

 may be detached and collected in the " ring- 

 net" (INTRODUCTION, p.xliv), and the pieces 

 of muslin placed in the bottles. A stick 

 with a loop of string at the end, is often 

 useful in procuring those which would be 

 otherwise beyond reach; the neck of the 

 bottle being engaged in the loop, and the 

 mouth kept downwards when immersed in 

 the water until opposite and close to the 

 masses of Diatomaceae, it is then inclined 

 upwards and filled. On exposing the bottles 

 to the light for some hours, the Diatomaceae 

 will collect on the surface of the mud or 

 other matters, and can then be removed with 

 a dipping-tube. It is often difficult to free 

 them from minute particles of sand; this 

 may, however, generally be done by diffusing 

 the deposit through distilled water, allowing 

 the mixture to stand for a short time, and 

 then pouring off the uppermost portions ; 

 the sand being the heaviest, will subside first. 

 The deep-sea species may be obtained by 

 dredging, or by treating the alimentary canal 

 of fishes, mollusca, &c., with strong nitric 

 acid as above directed. 



The Diatomaceae are often found fossil 

 (forming the fossil Infusoria of geologists) ; 

 occurring in vast numbers in aquatic and 

 marine geological deposits, forming hills, 

 rocks and various strata ; also in peat-beds, 

 fossil polishing powders, as tripoli, &c. The 

 deposits from San Fiore (Tuscany), Bermuda, 

 Lough Morne (Ireland), &c., are well known 

 as containing many of the most beautiful 

 species, and are sold by the dealers in micro- 

 scopic objects and apparatus. 



Preservation. The Diatomaceae may be 

 preserved either in the dry state, immersed 

 in balsam, in water, or dilute spirit (one to 

 six) (see PRESERVATION). For exhibiting 

 the delicate markings,they should be mounted 

 in the dry state, placed upon and covered by 

 the thinnest glass which can be obtained. 



The mounted sable-hair or bristle will be 

 essential in isolating single valves (INTRO- 

 DUCTION, p. xxii) for mounting. 



With regard to the systematic arrangement 

 of the Diatomaceae, the following table must 

 be regarded merely as an aid to finding the 

 genera scattered through the work ; the 

 structure of the frustules of many genera is 

 so imperfectly known, that it would be im- 



possible at present to institute a correct 

 systematic division. Those genera which are 

 fossil, or are not known to occur in Great 

 Britain, are appended after the line ( ). 



Tribe 1. Striata. Frustules transversely 

 striated ; neither vittate, nor areolate. 

 Subtribe 1 . Astomaticae. Valves without a 

 median nodule or aperture. 



Cohort 1. EUNOTI^E. Epithemia(Pl.\2. 

 fig. 32), Eunotia (PI. 18. fig. 30), Hi- 

 mantidium (PI. 12. fig. 36). 



Coh. 2. MERIDIEM. Meridian (PI. 12. 

 fig. 28; PI. 13. fig. 7). Oncosphenia. 



Coh. 3. FRAGILARI^E. Diatoma (PI. 12. 

 fig. 26), Fragilaria (PI. 12. fig. 33), Den- 

 ticula(Pl. 12.fig.25), Odontidium(Pl 13. 

 fig. 14). 



Coh. 4. MELOSIRE.E. Cyclotella (PI. 12. 

 figs. 21, 22), Melosira (PL 13. figs. 5, 6), 

 Orthosira (PI. 13. fig. 15), Pyxidicula 



(PI. 19. fig. 13). Dicladia, Gonio- 



thecium, Hercotheca, Insilella, Masto- 

 gonia, Periptera, Pododiscus (PI. 13. 

 fig. 16), Podosira(Pl. 14. fig. 27), Rhi- 

 zoselenia, Stephanodiscus, Stephanogo- 

 nia, Syringidium. 



Coh. 5. SURIRELLE.E. Bacillaria (PL 12. 

 fig. 14), Campylodiscus (PL 12. fig. 16; 

 P1.18.fig.44),Don/^ora(PL12.fig.29), 

 Nitzschia (PL 13. figs. 9-13), SpMncto- 

 cystis (PL 12. figs. 23, 24), Surirella 

 (PL 13, figs. 21, 22), Synedra (PL 13. 

 figs. 23-25), Tryblionella (PL 13. figs. 30- 

 32). Rhaphoneis. 



Subtribe 2. Stomaticse. Valves with a me- 

 dian nodule or aperture. 



Coh. 6. COCCONEID^B. Cocconeis(Pl.l2. 

 figs. 17, 18). 



Coh. 7- ACHNANTHE^E. AchnantUdium 

 (PL 12. figs. 5, 6), Achnanthes (PL 12. 

 figs. 1-4), Dickieia (PL 14. fig. 16), 

 Cymbosira (PL 14. fig. 18). 



Coh. 8. CYMBELLE.E. Cymbetta(Pl 18. 

 fig. 31), Cocconema (PL 12. figs. 19, 20), 



Encyonema (PL 14. fig. 10). Syncy- 



clia (PL 14. fig. 14). 



Coh. 9. GOMPHONEME^E. Gomphonema 

 (PL 12. fig. 34), Sphenella (PL 14. 

 fig. 19), Sphenosira (PL 13. fig. 26). 



Coh. 10. NAVICULE^E. Amphiprora (PL 

 12. fig. 8), Amphora (PL 12. figs. 10, 

 11), Pinnularia (PL 11. fig. 1-5), Navi- 

 cula(P\.ll.figs.6-9),Gyrosiffma (PL 11. 

 figs. 10-38), Stauroneis (PL 11. figs. 43, 

 46), Diadesmis (PL 12. fig. 27), Schizo- 

 nema (PL 14. fig. 12). Colletonema, 



