87 



but a triple-rayed form of Staurastnim tetracerum (Ralfs), ordi- 

 narily, however, occurring compressed. The number of rays or 

 angles in the end view of a Staurastrum, as is well known, is of 

 no importauce ; the same form occurs with sometimes three, 

 sometimes four or more angles (nay, sometimes with a different 

 number at either end of the same specimen), therefore whether 

 with two only or tiuee would seem to be equally of little real im- 

 portance, except that the reduction to two only is greatly more 

 rare. It is the character or kind of arras, not their number, 

 which is of importauce. Mr. Archer would not by any means, 

 however, go so far as Reinsch does in some cases. For instance, 

 that author regards Arthrodesmiis convergens (Meneghini), Ehr., 

 as but a variety of Staurastrum Dickiei (Ralfs), and he merges 

 the former into the latter, suppressing St. Dickiei. Altogether 

 Mr. Archer would reiterate the view he had before now expressed 

 (largely confirmed, he thought, by Dr. Barker's specimens in 

 another section of the genus), that Arthrodesmus convergens was 

 truly a two sided Staurastrvim, and should be placed in that genus, 

 so far coiucidiug with Reinsch ; but he could not acquiesce, on 

 the other hand, that it could be considered as but making up 

 with Staurastrum Dickiei one species only, for these two forms 

 are not only distinct in size and contour, but absolutely different 

 in their zygospores. Reinsch, indeed, takes no note of this latter 

 circumstance in this instance, though he considers it of import- 

 ance in other similar cases, so that, perhaps, he may hereafter 

 modify his view. In the form called Arthrodesmus convergens 

 the zygospore is large and absolutely destitute of spines, whilst 

 in Staurastrum Dickiei it is densely beset with subulate acute 

 spines. With regard to Dr. Barker's form, and the typical St. 

 gracile, there did not appear to be those material differences in 

 size and contour that exist between the two forms alluded to ; Dr. 

 Barker's seemed, indeed, to have a greater proportional distance 

 from extreme to extreme of the projecting processes than the tri- 

 angular form, but this would appear to arise from its being plane, 

 the observer thus seeing the whole distance nearly in one line, 

 whilst in the triangular form the two (of the three) processes in 

 view would be tixrned a little up towards the observer, thus 

 rendering the distance between their extremities apparently, not 

 really, shorter ; the absolute distance, if it could be measured by 

 traversing along the upper outer corner or edge of the top or end 

 of the Staurastrum, would be pretty much alike. There is no 

 doubt, however, so long as we are unacquainted with the zygo- 

 spores of those forms, as regards either view, we have not ex- 

 hausted the argument. 



imh August, 1869. 



Dr. John Barker showed two pretty forms of Spirulina, and, as 

 they writhed and twisted under the microscope, very singular 

 looking objects. Without venturing to say very certainly, these 

 Mr. Archer had some time ago identified as Spirulina Zanardinii 



