333 



DIATOMACE^E. 



DIATOMACE^E. 



334 



animals possessed of vessels but without a heart and pulsation, and pro - 

 vided with a simple tubular intestinal canal. The forma developed in 

 the highest degree in that division would be Holothuriae and Echinoidece. 

 " The minute forms of organic life in the rocks of Barbadoes, as far 

 as investigated by Professor Ehrenberg in February, 1847, consist of 

 the following groups : 



Species. 



Polycyatina, . . ' 282 



Polygastrica . '. '. '. '. '. 18 

 Phytolitheria . . . .- . .27 



Geolithia 27 



folythalamia 7 



361 

 Of these more than 300 are new forms. 



" The great discovery of the Polycystina, which might be almost 

 called a new class, since they amount to upwards of 280 species, a 

 larger number of specific forms than is contained in some classes of 

 animals, may guide us to form an idea of the geological age of the 

 rocks in Scotland district, by comparing these forms with similar 

 fossil animalcules from rocks upon the age of which geologists have 

 agreed. Ehrenberg considers that the Polycystina from the rocks 

 of Barbadoes resemble more the animalcules from rocks of the 

 secondary period than the tertiary." 



Amongst the varieties of quartz rock the mineralogist recognises, 

 under the name of tripoli and polishing powder, certain pulverulent 

 and earthy forms of silex. On placing these substances under the 

 microscope they are found to be entirely composed of the siliceous 

 frustules of Diatomacea. The polishing powder or slate (polirschiefer) 

 found at Bilin in Bohemia is used for the purpose of producing a 

 polish on fine surfaces. The angularity and hardness of the frustules 

 of the Diatoms well adapt them to this purpose. 



Another deposit in which the Diatomacea have been found in great 

 abundance is the Bergmehl of Sweden. [BERGMEHL.] The Diatoms 

 found by Ehrenberg in this formation are principally species of 

 ffavicula. (Fig. 6.) 



Amongst the tertiary deposits, beds of Diatomacete are very 

 common. They have been observed in Italy, in Germany, and in 

 several of the States of America. " The city of Richmond in Virginia 

 is said to be built upon a stratum of Diatomaceous remains, 18 

 feet in thickness." (Smith.) Professor Gregory of Edinburgh has 

 recently described, in the ' Transactions of the Microscopical Society,' 

 a Diatomaceous earth, discovered about two years ago by the Duke 

 of Argyll hi the Isle of Mull. It constitutes a bed resembling marl 

 in appearance, lying in a rough piece of ground between Loch Baa 

 and the sea. The lake is about 30 feet, the land about 40 feet, 

 above the sea-level. At one part there is a hollow, which in winter 

 used to become a small loch, in summer only a stagnant p >ol, and in 

 draining this the bed of marl was discovered. The bed rests upon 

 gravel, which appears to belong to the diluvial period, and the 

 Diatomaceous earth is probably of recent origin. Professor Gregory 

 has examined the contents of this earth with great care, and has 

 given a list of upwards of 130 species, which he has been able to 

 make out (' Quarterly Microscopical Journal,' January, 1854). Of 

 these upwards of 20 are altogether new species, or species that are 

 new in a British locality. 



From these facts it will be seen that the subject of fossil 

 Diatomacece promises an almost boundless field for further inquiry. 

 It appears that we may say of these organisms, what we can say of no 

 other family or group of organised beings, that once created they 

 exist for ever. Myriads of species of soft-bodied animals have 

 perished, never to be recognised, but each individual cell of the 

 Diatom leaves its siliceous wall as a record of its existence a record 

 that the ordinary forces of nature seem to have little or no power in 

 obliterating. 



We now turn to the subject of arrangement. It would of course 

 be impossible here to give any account of individual species, and 

 systematic arrangements are being constantly modified by new 

 discoveries. The following is an arrangement of the families or 

 tribes by Kiitzing : 



Tribe I. STRIAT.E. 



Order I. Aitomatictt. 



Without a central opening on the secondary valve. 

 * Transverse striaj unbroken. 

 Family 1. Eunotiece. 

 Family 2. Meridiece. 

 Family 3. PragUariecc. 



** Stria; broken (interrupted) in the median line. 

 Family 4. Meloteir&z. 

 Family 5. SurireUea. 



Order II. Stomatica. 

 With the central opening. 



a Monoitomaticce. 



Having a median aperture on only one of the two secondary 

 surfaces. 



Family 6. Cocconeidece. 

 Family 7. Achnanthece. 

 Distomaticce. 



With a median aperture on each secondary surface. 

 Family 8. Cymbellea. 

 Family 9. Gomphonemece. 

 Family 10. Naviculeoe, 



Tribe II. VITTATJS. 

 Order I. Astomaticce. 



Without central opening on secondary side. 

 Family 11. Licmophorece. 

 Family 12. Slriatelleie. 



Order II. Stomaticce. 



With a large distinct aperture. 



Family 13. Tdbellarieai. 



Tribe III. AREOLATJS. 

 Order I. Discifornes. 



Family 14. Coscinodiscea. 

 Family 15. Aitguliferce. 

 Family 16. Tripodiscece. 



Order II. Appendiculata. 

 Doubtful forms. 



Family 17. Blddidphicae. 

 Family 18. Angulatce. 

 Family 19. Actiniscece. 



The Rev. W. Smith, in his ' Synopsis of the British Diatomaceso,' 

 gives the following arrangement of the genera : 

 Tribe I. Frustules naked ; not imbedded in gelatine nor inclosed in 



membranaceous tubes. 



Sub-Tribe 1. Connecting membrane deciduous; frustules solitary, or 

 during self-division in pairs ; rarely in greater numbers, adherent 

 or free, dispersed, or aggregated into a mucous stratum. 

 22 Genera 



Epithemia (fy, 19) . . 16 species. 

 Eunotia (fig, 1) . . . . 7 species. 

 Cymbdla .... 6 species. 

 Amphora . . . . . 8 species. 

 Cocconeis . . 6 species. 



Coidnodiscus . . . . 3 species. 

 Eupodiicut (fy. 2) . . 5 species. 

 Actinocyclut . . . . 1 species. 

 Arachnodiscus ... 1 species. 

 Triceratium (fig. 3) . . . 3 species. 

 Cydotella .... 4 species. 

 Campylodiscus . . . . 7 species. 

 Surirella (fy. 4) . . .20 species. 

 TryUionella, . .'.. 6 species. 

 Cymatopleura ... 5 species. 

 Nitzschia . . . 23 species. 



Amphiprorct .... 5 species. 

 Amphipleura . . . . 2 species. 

 ffumcula (fig. 6) . . .36 species. 

 Pinnularia . . . . 24 species. 

 Stauroneis . . . .10 species. 

 Pleuroiigma (fig. 7) . . . 26 species. 



Sub-Tribe 2. Connecting membrane subpersistent ; frustules after 

 self-division attached by a gelatinous cushion, or dichotomous 

 stripes. 



7 genera 



Synedra (fig. 5) . . .24 species. 

 Dorypkora . . . . 2 species. 

 Cocconema (fig. 8) . . .4 species. 

 Gomphonema (fig. 9) . . . 12 species. 

 Podosphenia .... 5 species. 

 JUiipidophora . . . . 3 species. 

 Jjicmophora .... 2 species. 



Sub-Tribe 3. Connecting membrane evanescent, or obsolete ; frustules 

 after self-division united into a compressed filament. 

 12 Genera 



Meridian (fig. 10) . .2 species. 



Bacillaria (fig. 11) . . . 1 species. 

 Jfimantidium ... 7 species. 

 Odontidium . . . . 4 species. 

 Denticula .... 4 species. 

 Fragilaria . . . . 3 species. 

 Eucampia .... 1 species. 

 Achnanthet (fig. 12) . . . 6 species. 

 JJiadesmit .... 3 species. 

 Rhaitdanema . . . . 2 species. 

 Striatella (fig. 13) . . . 1 species. 

 Tetracyclv* . . . . 1 species. 



