ANIMAL NATURE OF DIATOMB^. 891 



also wanting to show that it consists of gum, starch, or 

 chlorophyll, which would be necessary were it a goniinic 

 substance, as advanced by Kiitzing ; and analogy even is 

 wanting, for we do not see, in any Alga, a similar dis- 

 position of the internal substance. The often quoted 

 resemblance to the Confervae cannot even be deemed 

 apparent ; for in no Confervae are distinct spherules met 

 so regularly, or disposed so symmetrically. During desic- 

 cation it happens in the marine species, as in the Podosirae 

 already described, that the internal substance adheres to 

 the inner wall in the form of oily globules surrounded 

 by a distinct, transparent margin, and compressed one 

 against another in the form of regular polygons. Ehren- 

 berg also speaks of diaphanous vesicular spaces, which he 

 regards as stomachs. Kiitzing enumerates, figures and 

 describes nineteen species, marine, freshwater, and fossil, 

 besides the four doubtful ones placed at the end, and the 

 famous ferruginea (M. oc/tracea, Ralfs,) which he proves 

 not to belong to the class of Diatomeae. 



We have a new species in the Euganean thermal 

 springs; this is so different from all the others, that it 

 might serve as the type of a separate genus, which, 

 meanwhile, I propose as a subgenus, with the name of 

 Pleurosira; articulis cylindricis non carinatis isthmo 

 laterali angulatim concatenatis. The specific description 

 will be as follows.- Melosira (Pleurosira) thermalis: major, 

 articulis cylindricis solitiariis, isthmo laterali angulatim 

 concatenatis, disco laterali levissimo. Hab. inter Clado- 

 phoras et Lyngbyas in thermis Euganeis temp. + 30 R. 



The diameter varies from ^ to -^ of a millimetre (5 to 

 8 centomillimetres). The length of the articulations is so 

 variable, that I did riot think it proper to mention it 

 .in the description. The shortest scarcely exceed the 

 diameter, but others are twice or thrice as long. In the 

 smaller specimens the interstitial ring exceeds a little in 

 breadth the two lateral circular bands which form part of 

 the secondary surfaces. A distinct and large circular 

 canal, evidently projecting into the internal cavity, and, 



