M. Miiller on Substances inclosed in Mochastones. 419 



up gradually with higher powers they appear as represented at 

 b — g ; they are of the same colour as the frond and lie scattered 

 upon it, as if pressed to it. They are tender, scale-like mem- 

 branes (?) jagged at the border. 



It is surprising to find structures like these, which are the last 

 one should expect to find upon what, judging from habit, I have 

 considered as a Nostoc. 



Many no longer retain their original orbicular form ; and more 

 are frequently torn into many divisions as at (e) . 



If we inquire what this formation probably is, it is very pleasing 

 to be able to give a certain answer : they are forms which belong 

 to the great family Desmidiacece amongst Algae, and indeed to the 

 genus Micrasterias. 



It has the greatest affinity with Micrasterias lacerata, Kiitzing, 

 and I leave it for a while to the judgement of algologists. 



Since hitherto Micrasterice are known only as hydrophytes, the 

 Nostoc must also be a water Alga. Found at Idar in the princi- 

 pality of Birkenfeldt. 



6. Fig. 4—9.— More or less round, pinnate, moss-like fronds, 

 with a yellow-brown substratum, in the middle of which is gene- 

 rally a circle with a dot in its centre. Under the microscope the 

 texture appears as in the foregoing, macerated, and we can there- 

 fore judge only from habit what the production may be. 



If we examine first the circle in its centre, with its own central 

 dot, it appears that this is the point to which the object was fast- 

 ened, and from whence as a centre the other branches proceeded. 

 It must have been gelatinous, more or less globose, as appears 

 from the gradually fading colour and the very thin compressed 

 membrane ; it must have been conglobated, so as to receive its 

 present orbicular form. The feather-like lines were branches, 

 whose branchlets were also gelatinous and conglobated. 



This again then belongs to the family of Alga?, being most 

 nearly allied to Chatophora amongst the Nostochinea , whose frond, 

 as in Chcet. endivitefolia, exhibits a similar branched structure. 

 Found in a clear chalcedony from Oberstein. 



7. Fig. 10. — Red organic masses, appearing to the naked eye as 

 small, more or less isolated dots, occurring in a clear chalcedony. 

 The circumjacent parts are yellow. This yellow field is bordered 

 by similar red dots, only larger and more distinct and tolerably 

 isolated. 



Under a weak magnifying power they appear like more or less 

 oval balls, generally very regular, sometimes much torn and 

 crushed, the one dark red, the other reddish yellow. 



As in fig. 2, a higher magnifying power surprises the inqui- 

 ring eye, when these dots, which still appear superficial and 

 isolated, are found to exhibit the forms represented in the 

 figures c — s. 



