ANIMAL NATURE OF DIATOMEjE. 389 



often happens that the two articulations are separated a 

 little from each other, and the external tube is then con- 

 tracted in the intermediate space, perhaps indicating the 

 origin of the isthmus. I never succeeded in observing 

 more pairs connected together. The stipes is little 

 inferior in length to the diameter of the articulation. 

 Longitudinal folds are always present, which I believe to 

 be six, since there are always four (at least ?) on each sur- 

 face. I have never succeeded in obtaining a sight of 

 that central aperture in the lateral surfaces, from which 

 Klitzing says he has seen the stipes to issue both in Podo- 

 sircB and MelosircB, especially the marine species. Finally, 

 I observe that within the articulation there appears an 

 open space, which is entirely owing to the internal sub- 

 stance, for it is destroyed wholly by fire or acids. 



14. Melosira. — Individua concatenata,adnafa. Lorica 

 bivalvis, vahce cingulo v. annulo interstifiali tenerrimo 

 maxime hyalino conjunctcB. 



" * Lysigonium. — Articulis globosis vel eJlipticis, prope 

 utrmiique finem carina annuliformi instructis." 



" ** Qallionella. — Articulis cylindricis, non carinatis." 



The Melosirm in general may be regarded as poly- 

 pariform associations of Cyclotellm, and the comparison" 

 prevails principally in the second sub-genus. The dis- 

 tinction of the two sub-genera is also proposed by Hassall 

 {SphtBrophora, Meloseira), but it is to Klitzing we are 

 indebted for establishing it upon the important character 

 of the carina, which occurs only in the first two species 

 {M. salina, M. nummuloides), a character on whose 

 organographic value we cannot decide anything, but 

 which merits some consideration in a morphological 

 point of view. For that projecting ring bounds the lateral 

 surfaces ; whilst in the other species, with sides more or 

 less convex, these are continuous, as it were, with the 

 primary surfaces. In all the species we may notice 

 the double furrovv- which forms a ring connecting the 

 body of each individual laterally to the interstitial ring ; 



