394 ANIMAL NATURE OF DIATOMEiE. 



development of the lateral surfaces prevails over that of 

 the primary ones, which we find finally to disappear in 

 certain genera {Pyxidicula, Podosira^ as well as in some 

 species of Melosira [varians, oricJtalcea), the increased 

 length of the articulations involving the corresponding 

 development of the primary surfaces. And it is to be 

 observed, that although in this family the primary sur- 

 faces differ precisely as much in form as they do in the 

 three preceding ones, yet we find in these the same 

 organic character as in the greater number of the other 

 genera, viz., the presence of longitudinal furrows or 

 canals. The separation of one lateral surface or valve 

 from the other, with the consequent dilatation of super- 

 ficies, which the primary surfaces exhibit before the du- 

 plication takes place (though verified to some degree in 

 other genera, yet in the MelosircB better than elsewhere), 

 presents an undeniable analogy with the reduplication of 

 Desmidiese, which Brebisaon distinguishes from the de- 

 duplication of Diatomese. The particular disposition of 

 the internal substance, the currents or mucous threads 

 radiating from a centre, the enlargement of some arti- 

 culations, and the dilatation of the interstitial ring, are 

 isolated facts, which however merit particular attention 

 in the paucity of our knowledge. 



15. Campylodiscus. — Individua singularia, discifor- 

 mia; discus curvatus vel tortuosus, rotundato-elUpticus 

 radiatus. 



Although I have hitherto only been able to examine 

 that one species of this. genus (C. clypeus,) which is 

 found in the fossil flour of Santa Fiore, in the kieselguhr 

 of Franzensbad, and constitutes the entire substance of 

 the tripoli of Eger, I think I can add something to 

 what Klitzing says of it. He indicates, indeed, in 

 fig. 5, the thickness of the margin, which, in this in- 

 stance, represents the primary surfaces uniting tt)getlier 

 into a continuous superficies, but neither in the other 

 figures nor in the description does he notice it any 



